Disallow squashing for blending layers.

Blending layers should have access to the backdrop, up to the nearest
stacking context. The squashing layer gets created in between
the blending layer and the backdrop, so that blending happens over
a clear transparent backdrop.

BUG=415895

Review URL: https://codereview.chromium.org/587173007

git-svn-id: svn://svn.chromium.org/blink/trunk@182428 bbb929c8-8fbe-4397-9dbb-9b2b20218538
bindings: Prefers SW::wrapperTypeInfo to V8T::wrapperTypeInfo.

Uses SW::wrapperTypeInfo rather than V8T::wrapperTypeInfo,
associateObjectWithWrapperNonTemplate rather than associateObjectWithWrapper.

This CL depends on http://crrev.com/590153002

BUG=235436

Review URL: https://codereview.chromium.org/593623004

git-svn-id: svn://svn.chromium.org/blink/trunk@182429 bbb929c8-8fbe-4397-9dbb-9b2b20218538