Fix PersistentHeapHashMap to work with stack allocated, heap backed weak collections

R=ager@chromium.org, sof@chromium.org
BUG=

Review URL: https://codereview.chromium.org/197343003

git-svn-id: svn://svn.chromium.org/blink/trunk@169131 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Resize EditFileSystemDialog on adding excluded row.

BUG=352038

Review URL: https://codereview.chromium.org/196353011

git-svn-id: svn://svn.chromium.org/blink/trunk@169132 bbb929c8-8fbe-4397-9dbb-9b2b20218538