Oilpan: move ImageBitmap to the oilpan heap.

R=haraken@chromium.org,erik.corry@gmail.com
BUG=340522

Review URL: https://codereview.chromium.org/190183003

git-svn-id: svn://svn.chromium.org/blink/trunk@169153 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add ASSERTS to FontTraits

Add ASSERTS ensuring that the unused bits in the mask are always unset.

TBR=eseidel@chromium.org
BUG=351734

Review URL: https://codereview.chromium.org/196973009

git-svn-id: svn://svn.chromium.org/blink/trunk@169154 bbb929c8-8fbe-4397-9dbb-9b2b20218538