Widget property sometimes fail to show its dartdoc when hovering over it

## Steps to Reproduce

The widget property won't display its dartdoc sometimes, when I hover over a widget property name in the detail pane of the inspector in Android Studio.


## Version info

[✓] Flutter (Channel master, v0.5.4-pre.5, on Mac OS X 10.13.4 17E202, locale en-US)
• Flutter version 0.5.4-pre.5 at /Users/taodong/Code/flutter_repos/flutter
• Framework revision 3019ad976d (71 minutes ago), 2018-06-11 11:31:25 -0700
• Engine revision d33bbff470
• Dart version 2.0.0-dev.60.0.flutter-a5e41681e5

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.0)
• Android SDK at /Users/taodong/Library/Android/sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-27, build-tools 27.0.0
• 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-1024-b01)
• All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.3.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 9.3.1, Build version 9E501
• ios-deploy 1.9.2
• CocoaPods version 1.5.2

[✓] Android Studio (version 3.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 25.0.1
• Dart plugin version 173.4700
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[!] VS Code (version 1.23.1)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension not installed; install from
https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[✓] Connected devices (1 available)
• iPhone 6s • 713F5DD5-D1A0-46ED-976D-3D1487DBCFC6 • ios • iOS 11.3 (simulator)

Reproduce the missing dartdoc by hovering over widget properties in the Android Studio Inspector detail pane, using the Flutter plugin and Dart plugin versions described. Trace the inspector-to-dartdoc behavior and verify that the property's documentation appears consistently when the issue is fixed.

Written by the indexing model from the issue text.