Deflake inspector layer tests

- add quietUntilDone flag that suppresses inspector test output till test is
    done, so output does not interfere with layout & co;
- only install LayerTreeChanged event listener after we actually schedule tree
    update to avoid stray events;
- drop testRunner.display() and use requestAnimationFrame to avoid multiple
   tree changes being coalesced.
- speed up layer-compositing-reasons.html by parallelizing all queries.

Review URL: https://codereview.chromium.org/149273003

git-svn-id: svn://svn.chromium.org/blink/trunk@166038 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make naming of calculateScrollbarModesForLayout reflect it has side effects.

The current name makes it sound like it's just going to calculate the scrollbar
modes. The code also resets the m_viewportRenderer pointer. Update the name to
be calculateScrollbarModesForLayoutAndSetViewportRenderer to make it clearer
there are side effects if using/moving this call.

BUG=

Review URL: https://codereview.chromium.org/148393004

git-svn-id: svn://svn.chromium.org/blink/trunk@166039 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use PartitionAlloc for fastMalloc on Android

This switches fastMalloc to PartitionAlloc for Android. Previously, we only
used PartitionAlloc for fastMalloc on Mac OS X.

BUG=312725
R=tonyg@chromium.org

Review URL: https://codereview.chromium.org/148013010

git-svn-id: svn://svn.chromium.org/blink/trunk@166040 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use stricter typing for HTMLCollection named getter

Use stricter typing for HTMLCollection named getter. According to specification,
it should return an Element, not a Node. This CL updates the IDL and the native
side to explicitly use Element type.

There is no Web-Exposed behavior change. The stricter typing just makes clearer
what kind of Nodes we are dealing with.

R=haraken, adamk

Review URL: https://codereview.chromium.org/148013008

git-svn-id: svn://svn.chromium.org/blink/trunk@166041 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Unreviewed gardening. Pixel diffs on scrollbar arrows.

The baselining for this appears to vary by particular windows
platform, so I'm adding "Pass" for now.

TBR=tkent@chromium.org,ojan@chromium.org
BUG=335472

Review URL: https://codereview.chromium.org/149093007

git-svn-id: svn://svn.chromium.org/blink/trunk@166042 bbb929c8-8fbe-4397-9dbb-9b2b20218538