Handle null return value for getLastResortFallbackFont

getNonRetainedLastResortFallbackFont can, despite the name which seems
to suggest otherwise, return 0. Handle this case by bailing out and
asserting.

BUG=341628
R=dglazkov@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166678

Review URL: https://codereview.chromium.org/150103014

git-svn-id: svn://svn.chromium.org/blink/trunk@166740 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Lazy save in GraphicsContext.

Investigation reveals that code frequently calls GraphicsContext::save
and then another save or restore with no state changes at all. State
saves are not cheap (they currently heap allocate a state object and
copy all the elements from the current state).

We should lazy save and we should attempt to avoid the allocations.
In a follow-up patch we will maintain a current SkPaint object for each
state, to avoid repeatedly setting up paint. This will add even more
cost to state save (to benefit all draw calls with that state) so it is
important we address this issue.

R=senorblanco,fmalita
BUG=334904

Review URL: https://codereview.chromium.org/137783014

git-svn-id: svn://svn.chromium.org/blink/trunk@166741 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove scrollbars from two layout tests.

These tests started failing after a scrollbar-related change, but they
are not intended to test scrollbar behavior, so add "body { overflow:
hidden; }" to avoid this source of brittleness.

BUG=341145
NOTRY=true

Review URL: https://codereview.chromium.org/137823013

git-svn-id: svn://svn.chromium.org/blink/trunk@166742 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Auto-rebaseline for r166619

http://src.chromium.org/viewvc/blink?view=revision&revision=166619

BUG=339852,339090,339806
TBR=fmalita@chromium.org

Review URL: https://codereview.chromium.org/158003002

git-svn-id: svn://svn.chromium.org/blink/trunk@166743 bbb929c8-8fbe-4397-9dbb-9b2b20218538