DevTools: Get rid of greenish for JS frames on timeline

BUG=363976
TBR=pfeldman

Review URL: https://codereview.chromium.org/247713005

git-svn-id: svn://svn.chromium.org/blink/trunk@172392 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Don't always repaint on zIndex change

If zIndex of a composited layer changes and there is no other conditions
triggering repaint, we should not repaint the layer.

Now treat zIndex change like opacity change about repainting.

BUG=364636,365865
TEST=reuse existing compositing/repaint/should-not-repaint-composited-descendants.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=171989

Review URL: https://codereview.chromium.org/240253007

git-svn-id: svn://svn.chromium.org/blink/trunk@172393 bbb929c8-8fbe-4397-9dbb-9b2b20218538