Remove content dependencies from RenderWidgetCompositor.

This will allow us to move it to blink platform.

IsUseZoomForDSFEnabled() is moved to CompositorDependencies,
and all callsites in content/renderer/ are changed to use
the CompositorDependencies. RenderViewImpl tests are set up
to override CompositorDependencies instead of injecting
command lines into their process.

R=piman@chromium.org

Bug: 838693
Change-Id: Ibccc88af3460d33a092228b95c230ef0236ff408
Reviewed-on: https://chromium-review.googlesource.com/1125172


Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572617}