Linux_android_emu external_textures_integration_test flakey

This test was recently fixed so it wasn't failing in `bringup`, but it appears to be flakey:

```
[2026-09-11 20:31:12.308834] [STDOUT] stdout: [+8069 ms] I/flutter ( 6193): Stopping 2x speed test...
[2026-09-11 20:31:12.970842] [STDOUT] stdout: [ +662 ms] +0 -1: renders frames from the device at a rate similar to the frames produced [E]
[2026-09-11 20:31:12.971901] [STDOUT] stdout: [ +1 ms] Expected: a numeric value within <5.0> of <49.4>
[2026-09-11 20:31:12.972045] [STDOUT] stdout: [ ] Actual: <42.5>
[2026-09-11 20:31:12.972169] [STDOUT] stdout: [ ] Which: differs by <6.899999999999999>
[2026-09-11 20:31:12.979002] [STDOUT] stdout: [ +6 ms] package:matcher/src/expect/expect.dart 187:31 fail
[2026-09-11 20:31:12.979472] [STDOUT] stdout: [ ] package:matcher/src/expect/expect.dart 182:3 _expect
[2026-09-11 20:31:12.979882] [STDOUT] stdout: [ ] package:matcher/src/expect/expect.dart 65:3 expect
[2026-09-11 20:31:12.980326] [STDOUT] stdout: [ ] test_driver/frame_rate_main_test.dart 67:5 main.
[2026-09-11 20:31:12.980758] [STDOUT] stdout: [ ] ===== asynchronous gap ===========================
[2026-09-11 20:31:12.981723] [STDOUT] stdout: [ ] package:test_api/src/backend/declarer.dart 253:15 Declarer.test..
[2026-09-11 20:31:12.981753] [STDOUT] stdout: [ ] ===== asynchronous gap ===========================
[2026-09-11 20:31:12.981766] [STDOUT] stdout: [ ] package:test_api/src/backend/declarer.dart 250:11 Declarer.test.
[2026-09-11 20:31:12.981774] [STDOUT] stdout: [ ] ===== asynchronous gap ===========================
[2026-09-11 20:31:12.981782] [STDOUT] stdout: [ ] package:test_api/src/backend/invoker.dart 318:9 Invoker._waitForOutstandingCallbacks.
[2026-09-11 20:31:12.994434] [STDOUT] stdout: [ +12 ms] +0 -1: Some tests failed.
[2026-09-11 20:31:12.995702] [STDOUT] stdout: [ +1 ms] Consider enabling the flag chain-stack-traces to receive more detailed exceptions.
[2026-09-11 20:31:12.995732] [STDOUT] stdout: [ ] For example, 'dart test --chain-stack-traces'.
[2026-09-11 20:31:12.997167] [STDOUT] stderr: [ +1 ms] Unhandled exception:
[2026-09-11 20:31:12.997192] [STDOUT] stderr: [ ] Dummy exception to set exit code.
[2026-09-11 20:31:13.044846] [STDOUT] stdout: [ +47 ms] Unregistering signal handlers...
[2026-09-11 20:31:13.047497] [STDOUT] stdout: [ +2 ms] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 shell screencap -p /data/local/tmp/flutter_screenshot.png
[2026-09-11 20:31:13.363467] [STDOUT] stdout: [ +315 ms] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 pull /data/local/tmp/flutter_screenshot.png /b/s/w/ir/x/w/rc/flutter_logs_dir/drive_03.png
[2026-09-11 20:31:13.374244] [STDOUT] stdout: [ +11 ms] /data/local/tmp/flutter_screenshot.png: 1 file pulled, 0 skipped. 49.1 MB/s (61931 bytes in 0.001s)
[2026-09-11 20:31:13.374288] [STDOUT] stdout: [ ] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 shell rm /data/local/tmp/flutter_screenshot.png
[2026-09-11 20:31:13.397285] [STDOUT] stdout: [ +22 ms] Screenshot written to /b/s/w/ir/x/w/rc/flutter_logs_dir/drive_03.png
[2026-09-11 20:31:13.398108] [STDOUT] stdout: [ ] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 shell am force-stop io.flutter.externalui
[2026-09-11 20:31:13.398129] [STDOUT] stdout: [ ] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 shell am force-stop io.flutter.externalui
[2026-09-11 20:31:13.449676] [STDOUT] stdout: [ +50 ms] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 uninstall io.flutter.externalui
[2026-09-11 20:31:13.449738] [STDOUT] stdout: [ ] executing: /b/s/w/ir/cache/android/sdk/platform-tools/adb -s emulator-5554 uninstall io.flutter.externalui
[2026-09-11 20:31:13.794828] [STDOUT] stdout: [ +342 ms] Success
[2026-09-11 20:31:13.798387] [STDOUT] stdout: [ +6 ms] "flutter drive" took 66,327ms.
[2026-09-11 20:31:13.806249] [STDOUT] stderr: [ +7 ms]
[2026-09-11 20:31:13.808446] [STDOUT] stderr: #0 throwToolExit (package:flutter_tools/src/base/common.dart:34:3)
[2026-09-11 20:31:13.808476] [STDOUT] stderr: #1 DriveCommand.runCommand (package:flutter_tools/src/commands/drive.dart:438:9)
[2026-09-11 20:31:13.808484] [STDOUT] stderr:
[2026-09-11 20:31:13.808492] [STDOUT] stderr: #2 FlutterCommand.run. (package:flutter_tools/src/runner/flutter_command.dart:1304:27)
[2026-09-11 20:31:13.808500] [STDOUT] stderr:
[2026-09-11 20:31:13.808507] [STDOUT] stderr: #3 AppContext.run. (package:flutter_tools/src/base/context.dart:154:19)
[2026-09-11 20:31:13.808515] [STDOUT] stderr:
[2026-09-11 20:31:13.808522] [STDOUT] stderr: #4 CommandRunner.runCommand (package:args/command_runner.dart:212:13)
[2026-09-11 20:31:13.808530] [STDOUT] stderr:
[2026-09-11 20:31:13.808538] [STDOUT] stderr: #5 FlutterCommandRunner.runCommand. (package:flutter_tools/src/runner/flutter_command_runner.dart:636:9)
[2026-09-11 20:31:13.808547] [STDOUT] stderr:
[2026-09-11 20:31:13.808554] [STDOUT] stderr: #6 AppContext.run. (package:flutter_tools/src/base/context.dart:154:19)
[2026-09-11 20:31:13.808562] [STDOUT] stderr:
[2026-09-11 20:31:13.808570] [STDOUT] stderr: #7 FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:571:5)
[2026-09-11 20:31:13.808578] [STDOUT] stderr:
[2026-09-11 20:31:13.808585] [STDOUT] stderr: #8 FlutterCommandRunner.run (package:flutter_tools/src/runner/flutter_command_runner.dart:355:5)
[2026-09-11 20:31:13.808592] [STDOUT] stderr:
[2026-09-11 20:31:13.808600] [STDOUT] stderr: #9 run.. (package:flutter_tools/runner.dart:150:11)
[2026-09-11 20:31:13.808608] [STDOUT] stderr:
[2026-09-11 20:31:13.808620] [STDOUT] stderr: #10 AppContext.run. (package:flutter_tools/src/base/context.dart:154:19)
[2026-09-11 20:31:13.808627] [STDOUT] stderr:
[2026-09-11 20:31:13.808634] [STDOUT] stderr: #11 main (package:flutter_tools/executable.dart:113:3)
[2026-09-11 20:31:13.808640] [STDOUT] stderr:
[2026-09-11 20:31:13.808646] [STDOUT] stderr:
[2026-09-11 20:31:13.808652] [STDOUT] stderr:
[2026-09-11 20:31:13.814645] [STDOUT] stdout: [ +6 ms] Running 2 shutdown hooks
[2026-09-11 20:31:13.814681] [STDOUT] stdout: [ ] Shutdown hooks complete
[2026-09-11 20:31:13.814689] [STDOUT] stdout: [ ] exiting with code 1
[2026-09-11 20:31:13.847553] [STDERR] Task failed: Executable "/b/s/w/ir/x/w/rc/tmpwst80tbb/flutter sdk/bin/flutter" failed with exit code 1.
[2026-09-11 20:31:13.847648] [STDERR]
[2026-09-11 20:31:13.847667] [STDERR] Stack trace:
[2026-09-11 20:31:13.880272] [STDERR] package:flutter_devicelab/framework/utils.dart 111:3 fail
[2026-09-11 20:31:13.880537] [STDERR] package:flutter_devicelab/framework/utils.dart 385:5 _execute
[2026-09-11 20:31:13.880567] [STDERR] ===== asynchronous gap ===========================
[2026-09-11 20:31:13.880574] [STDERR] dart:async Zone.registerBinaryCallback
[2026-09-11 20:31:13.880582] [STDERR] package:flutter_devicelab/framework/framework.dart 308:28 _TaskRunner._performTask.
[2026-09-11 20:31:13.880589] [STDERR] package:stack_trace Chain.capture
[2026-09-11 20:31:13.880596] [STDERR] package:flutter_devicelab/framework/framework.dart 306:11 _TaskRunner._performTask
[2026-09-11 20:31:13.880603] [STDERR] package:flutter_devicelab/framework/framework.dart 199:43 _TaskRunner.run
[2026-09-11 20:31:13.880610] [STDERR]
```

Start with test_driver/frame_rate_main_test.dart, especially the “renders frames from the device at a rate similar to the frames produced” test and its frame-rate assertion. Reproduce the Linux Android emulator failure and inspect the external-textures integration test setup around the reported timing. Done means the test reliably reflects the intended frame-rate behavior without intermittent failures.

Written by the indexing model from the issue text.