Move the scroll corner logic to RenderLayerScrollableArea

This change moves m_scrollCorner and the associated logic
to the new class. paintScrollCorner is kept as a shim as
it is called from RenderLayerBacking and we don't want to
make it aware of the split yet.

BUG=260899

Review URL: https://chromiumcodereview.appspot.com/23567047

git-svn-id: svn://svn.chromium.org/blink/trunk@158139 bbb929c8-8fbe-4397-9dbb-9b2b20218538
De-flakify http/tests/xmlhttprequest/origin-whitelisting-https.html

This started flakily failing with http://src.chromium.org/viewvc/blink/?revision=158065&view=revision.
The memory cache is provided results some but not all of the time, which is
changing the text output. This patch makes sure the urls are sufficiently
different that cache hits aren't an issue.

BUG=295538

Review URL: https://chromiumcodereview.appspot.com/24088013

git-svn-id: svn://svn.chromium.org/blink/trunk@158140 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove DecayArray & HasTrivialConstructor / Destructor

All this code was never used everywhere. DecayArray was an effort
to merge OwnPtr and OwnArrayPtr (https://webkit.org/b/75737) but
it never took off. This change didn't remove the Remove* functions
used only by DecayArray as they could be useful (and we would
remove most of the TypeTraits if we removed the unused functions).

Review URL: https://chromiumcodereview.appspot.com/24302002

git-svn-id: svn://svn.chromium.org/blink/trunk@158141 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add quirk to disable overflow: hidden on main frame for Android WebView.

This feature wasn't supported on classic WebView and many apps
turn out to put one on their body element without intending to
disable scrolling.  This quirk will only apply to apps targeting an
older SDK version than the current one.

NOTRY=true
BUG=295287

Review URL: https://chromiumcodereview.appspot.com/23484064

git-svn-id: svn://svn.chromium.org/blink/trunk@158142 bbb929c8-8fbe-4397-9dbb-9b2b20218538