Outline is not invalidated correctly

r169659 moved the outline to the visual overflow but forgot
that any outline change (especially growth) would impact the
visual overflow but would NOT trigger a layout.

The fix is to force a full layout when the outline changes.
It is not strictly necessary as we could get away with
just recomputing the visual overflow but we don't
have such a specialized layout yet.

BUG=3555983

Review URL: https://codereview.chromium.org/216013004

git-svn-id: svn://svn.chromium.org/blink/trunk@171162 bbb929c8-8fbe-4397-9dbb-9b2b20218538
ScrollingCoordinator::reset needs to unhook content layers

This function is only used in test code, and blindly deletes content
layers without informing their associated GraphicsLayers that they've
disappeared. This can lead to test crashes.

BUG=357292

Review URL: https://codereview.chromium.org/230823004

git-svn-id: svn://svn.chromium.org/blink/trunk@171163 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add a sizes attribute runtime flag

BUG=357586

Review URL: https://codereview.chromium.org/230973002

git-svn-id: svn://svn.chromium.org/blink/trunk@171164 bbb929c8-8fbe-4397-9dbb-9b2b20218538