Add a WebWidget::paintCompositedDeprecated.

This method is implemented by WebViewImpl and paints a composited
WebViewImpl into a canvas using the legacy software mode mechanisms.

This will be called by RenderViewImpl::didTapMultipleTargets on android
only, and will replace the enum value of
ForceSoftwareRenderingAndIgnoreGPUResidentContent.

R=abarth, enne
BUG=251960

Review URL: https://codereview.chromium.org/269723008

git-svn-id: svn://svn.chromium.org/blink/trunk@173321 bbb929c8-8fbe-4397-9dbb-9b2b20218538