8605 Allow building without python2 (cla: yes)

8608 [fuchsia] Fix SceneUpdateContext for new PaintContext field (cla: yes)

8611 Add FLEPluginRegistry for macOS (cla: yes)

8612 Remove call to SkFont::setLinearMetrics (cla: yes)

8615 Rename flow namespace to flutter (cla: yes)

8616 Add a unit test for PhysicalShapeLayer (cla: yes)

8617 Fixes a typo in comment (affects: docs, cla: yes)

8618 Test saving compilation traces. (cla: yes)

8621 Avoid manually shutting down engine managed isolates. (cla: yes)