Revert 162842 "Replace MakeWeak with SetWeak API in DOMWrapperMap"

> Replace MakeWeak with SetWeak API in DOMWrapperMap
> 
> BUG=324225
> R=marja@chromium.org
> 
> Review URL: https://codereview.chromium.org/95003003

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/95753002

git-svn-id: svn://svn.chromium.org/blink/trunk@162856 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add repaint layout tests.

These layout tests test to make sure we're only painting what's changed in
the flexbox case.

BUG=308701

Review URL: https://codereview.chromium.org/33743008

git-svn-id: svn://svn.chromium.org/blink/trunk@162857 bbb929c8-8fbe-4397-9dbb-9b2b20218538