Revert of Handle null return value for getLastResortFallbackFont (https://codereview.chromium.org/150103014/)

Reason for revert:
Appears to have triggered an ASSERT in org.chromium.android_webview.test.AwSettingsTest#testLayoutAlgorithmWithTwoViews

See androidwebview_instrumentation_tests in this build:

http://build.chromium.org/p/chromium.webkit/builders/Android%20Tests%20%28dbg%29/builds/17264



Original issue's description:
> 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

TBR=dglazkov@chromium.org,eseidel@chromium.org,eae@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=341628

Review URL: https://codereview.chromium.org/157723002

git-svn-id: svn://svn.chromium.org/blink/trunk@166727 bbb929c8-8fbe-4397-9dbb-9b2b20218538