Fix shadowed variables in the content layer.

Shadowed variables can make code harder to read. Don't support them
in the content layer.

BUG=794619

This CL was uploaded by git cl split.

R=fsamuel@chromium.org

Change-Id: Id33101d8feb26d33e4b3c8301bfb496bd9535298
Reviewed-on: https://chromium-review.googlesource.com/924163Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537673}

content/browser/renderer_host/delegated_frame_host.cc

@@ -420,7 +420,6 @@ void DelegatedFrameHost::SubmitCompositorFrame(
     skipped_frames_ = false;
 
     // Give the same damage rect to the compositor.
-    viz::RenderPass* root_pass = frame.render_pass_list.back().get();
     root_pass->damage_rect = gfx::Rect(frame_size);
   }