Stop scrolling the console to the bottom when multiple errors are shown

## Steps to Reproduce

- Run this app: https://github.com/InMatrix/flutter_error_studies/
- Tap "Unbounded Viewport" in the homepage of the app
- Observe output in the logging console

The first error is the root cause, and all subsequent errors are derivative. [The full log](https://gist.github.com/InMatrix/96ea88fc67b0f47a6a259c745509e5ba) has 655 lines with the "show structured error" setting on. The logging console will scroll to the bottom automatically. I need to then scroll back to the top. It would be more difficult if I had existing content in the console before this error occurred.

## Version info
[✓] Flutter (Channel stable, v1.7.8+hotfix.4, on Mac OS X 10.14.6 18G87, locale en-US)
• Flutter version 1.7.8+hotfix.4
• Framework revision 20e59316b8 (4 weeks ago), 2019-07-18 20:04:33 -0700
• Engine revision fee001c93f
• Dart version 2.4.0

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
• Android SDK
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-28, build-tools 28.0.3
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 10.2.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 10.2.1, Build version 10E1001
• CocoaPods version 1.7.2

[✓] iOS tools - develop for iOS devices
• ios-deploy 1.9.4

[✓] Android Studio (version 3.4)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 38.0.1
• Dart plugin version 183.6270
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)

[✓] IntelliJ IDEA Community Edition (version 2019.1.3)
• IntelliJ at /Applications/IntelliJ IDEA CE.app
• Flutter plugin version 38.0.3
• Dart plugin version 191.8348

[✓] VS Code (version 1.35.1)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 2.25.1