Repository: flutter
Issue: NetworkImage does not throw NetworkImageLoadException in widget tests on chrome platform
Labels: a: tests,engine,platform-web,a: error message,has reproducible steps,P2,found in release: 3.7,found in release: 3.9,team-web,triaged-web

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## Steps to Reproduce

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1. Pump a NetworkImage widget in a widget test

```
await tester.pumpWidget(NetworkImage(/* an image url */);
```

2. An `NetworkImageLoadException` should be thrown (in the default test platform), but on the Chrome platform no exception is thrown.

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**Target Platform:** Web
**Target OS version/browser:** Chrome
**Devices:**


## Logs

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     Run `flutter analyze` and attach any output of that command below.
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```
Analyzing app_flutter...                                                

   info • Unused import: 'dart:ui' • lib/generated_plugin_registrant.dart:4:8 • unused_import

1 issue found. (ran in 2.0s)
```

<!-- Finally, paste the output of running `flutter doctor -v` here. -->

```
[✓] Flutter (Channel master, v1.10.15-pre.378, on Linux, locale en_US.UTF-8)
    • Flutter version 1.10.15-pre.378 at /usr/local/google/home/chillers/flutter
    • Framework revision bf45897f13 (6 days ago), 2019-11-01 11:30:58 -0700
    • Engine revision 8ea19b1c76
    • Dart version 2.6.0 (build 2.6.0-dev.8.2 bbe2ac28c9)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at /usr/local/google/home/chillers/Android/Sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-stable, build-tools 29.0.2
    • Java binary at: /opt/android-studio-with-blaze-3.4/jre/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b16-5323222)
    • All Android licenses accepted.

[✓] Chrome - develop for the web
    • Chrome at google-chrome

[!] Android Studio (version 3.4)
    • Android Studio at /opt/android-studio-with-blaze-3.4
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b16-5323222)

[✓] IntelliJ IDEA Ultimate Edition (version 2019.1)
    • IntelliJ at /opt/intellij-ue-2019.1
    • Flutter plugin version 39.0.2
    • Dart plugin version 191.8423

[✓] VS Code (version 1.39.2)
    • VS Code at /usr/share/code
    • Flutter extension version 3.6.0

[✓] Connected device (2 available)
    • Chrome     • chrome     • web-javascript • Google Chrome 78.0.3904.97
    • Web Server • web-server • web-javascript • Flutter Tools

! Doctor found issues in 1 category.
```