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This patch adds the posting of important messages to the parent thread.
The messages are send when:
 - a lottie animation is initialized.
 - a lottie animation has started playing.
 - a lottie animation has resized its canvas.

This patch also fixes the lint for the wrapper code to be closer to
chromium's style guide.

Change-Id: Ibf27da53ec4bba6ec696041e312c7fb317a64833
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1747195
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Mitsuru Oshima (OOO 8/12,13) <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686507}