Add --force-compositing-mode to the text-drawing virtual suites.

This adds it to the linux-subpixel, windows-directwrite, and
mac-antialiasedtext virtual test suites.

R=enne, ojan
BUG=361729

Review URL: https://codereview.chromium.org/279973002

git-svn-id: svn://svn.chromium.org/blink/trunk@173788 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove the composited path from WebViewImpl::paint().

Now that we have WebWidget::compositeAndReadbackAsync() for layout
tests and WebWidget::paintCompositedDeprecated() for android, the
WebWidget::paint() method is only used for actually painting into
a GraphicsContext when the WebViewImpl is not composited.

Remove the composited path from this method and ASSERT that the
WebViewImpl is not being composited. Also remove the
WebViewImpl::doPixelReadbackToCanvas().

Depends on: https://codereview.chromium.org/266243002/
Depends on: https://codereview.chromium.org/276003002/

R=abarth, enne, aelias
BUG=251960, 365810

Review URL: https://codereview.chromium.org/264713014

git-svn-id: svn://svn.chromium.org/blink/trunk@173789 bbb929c8-8fbe-4397-9dbb-9b2b20218538