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Currently a PaintOp is not necessary rejected even if its drawing
canvas has a size of (0, 0). This should not be the case, for
performance purpose, we should just skip this draw op.

In PS#1, I added a test which fails without any code change,
to indicate that we are not reject a PaintOp even if the canvas
has size of 0.

In PS#3, I added code changes to make the test pass. The
code change ensures that if the paint rect is empty, then
it should be skipped.

Bug: 1157152
Change-Id: I28110c26e838c917326df82bf1debdc67ca5b50d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2585628
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836660}