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Many of the widgets that use CustomPaint were spamming repaints because CustomPaint repaints when the identity of the onPaint callback changes, which it does every build for StatelessComponents. This patch changes CustomPaint to use a CustomPainter, similar to the new custom layout widgets. The CustomPainter has a `shouldRepaint` function along with its `paint` function. This function gives clients explicit control over when the custom paint object repaints.
Small examples of the Flutter widget framework
To run these, open a terminal in this directory and use the following command:
flutter start --checked -t foo.dart
...where foo.dart is the file you want to run.