Completely removed the Extensions3D class (Take 2)

This WebKit-era abstraction serves no useful purpose in the context of blink.
Previous CL failed due to lingering Android dependencies.

BUG=326382
TBR=kbr@chromium.org, jamesr@chromium.org

Review URL: https://codereview.chromium.org/127163003

git-svn-id: svn://svn.chromium.org/blink/trunk@164714 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rework margin-collapsing for self-collapsing blocks
Refactor the way self-collapsing blocks with clearance are positioned so that they
get the correct logical-top position during margin-collapsing.

See also webkit.org/b/119979
BUG=309294

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=163454

Review URL: https://codereview.chromium.org/75133007

git-svn-id: svn://svn.chromium.org/blink/trunk@164715 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove unused executive.kill_all() method from webkitpy.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/127043003

git-svn-id: svn://svn.chromium.org/blink/trunk@164720 bbb929c8-8fbe-4397-9dbb-9b2b20218538