The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/89df64fbe6300c209e5a3f7e2f7a30a51be8b706

commit 89df64fbe6300c209e5a3f7e2f7a30a51be8b706
Author: trchen <trchen@chromium.org>
Date: Tue Dec 20 22:05:54 2016

[SPv2] Disable CompositingRecorder collapsing for SPv2

CompositingRecorder collapses its begin/end display items if there is only
one drawing display item in between. This won't work if the display item
may be layerized and the compositing operation is backdrop-dependent.

For example:

<drawing content="X"/>
<composite blend=multiply>
  <drawing content="Y"/>
</composite>

Will be collapsed as:

<drawing content="X"/>
<drawing content="saveLayer(blend=multiply); Y; restore();"/>

However the result will be incorrect if the second drawing display item gets
layerized.

This CL disables this optimization in SPv2.

BUG= 674805 , 675805 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2580143003
Cr-Commit-Position: refs/heads/master@{#439887}

[modify] https://crrev.com/89df64fbe6300c209e5a3f7e2f7a30a51be8b706/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
[modify] https://crrev.com/89df64fbe6300c209e5a3f7e2f7a30a51be8b706/third_party/WebKit/Source/core/paint/PaintControllerPaintTest.cpp
[modify] https://crrev.com/89df64fbe6300c209e5a3f7e2f7a30a51be8b706/third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp