Oilpan: Remove all the RefPtrs and most of the raw pointers to style
sheets.

Comment on the cases where the raw pointers cannot be removed at this point.

Leave the raw pointers in inspector/ alove. They are safe as they are
now because the inspector leaks all the CSSStyleSheets it is inspecting
via Persistent handles at this point (and used to leak them all via
RefPtrs.)

R=erik.corry@gmail.com, haraken@chromium.org, oilpan-reviews@chromium.org, vegorov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/199013003

git-svn-id: svn://svn.chromium.org/blink/trunk@169250 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove display() call from squashing LayoutTest

This test was calling display, as the animated gif would only invalidate
during paint calls.  This is a bit dodgy, as it relies on timing of the
gif and can't work unless an actual paint() occurs.

The test is trying to make sure that a non-CLM-owning layer inside of a
squashed layer only invalidates that layer and not more.  Therefore, a
change like updating the background color should be sufficient to verify
the same code.

BUG=345027

Review URL: https://codereview.chromium.org/199633002

git-svn-id: svn://svn.chromium.org/blink/trunk@169251 bbb929c8-8fbe-4397-9dbb-9b2b20218538