Make CompositorImpl::CompositeAndReadback fail and return false.

Removes the call to LayerTreeHost::CompositeAndReadback and just fail
immediately. This method should be replaced with an async readback
in order to get pixels again.

R=powei
BUG=252046

Review URL: https://codereview.chromium.org/273113004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269931 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/compositor_impl_android.cc

@@ -368,10 +368,7 @@ void CompositorImpl::SetHasTransparentBackground(bool flag) {
 }
 
 bool CompositorImpl::CompositeAndReadback(void *pixels, const gfx::Rect& rect) {
-  if (host_)
-    return host_->CompositeAndReadback(pixels, rect);
-  else
-    return false;
+  return false;
 }
 
 cc::UIResourceId CompositorImpl::GenerateUIResourceFromUIResourceBitmap(