cc: Stop passing the unused opaque rect out-param to blink.

Blink now has methods that don't take the rect out-param so use those.
Then we can delete the old methods with the out-param in blink.

R=vmpstr
BUG=413479

Review URL: https://codereview.chromium.org/572873005

Cr-Commit-Position: refs/heads/master@{#295092}

cc/blink/web_content_layer_impl.cc

@@ -54,12 +54,10 @@ void WebContentLayerImpl::PaintContents(
   if (!client_)
     return;
 
-  blink::WebFloatRect web_opaque;
   client_->paintContents(
       canvas,
       clip,
       can_use_lcd_text_,
-      web_opaque,  // TODO(danakj): Remove this.
       graphics_context_status == ContentLayerClient::GRAPHICS_CONTEXT_ENABLED
           ? blink::WebContentLayerClient::GraphicsContextEnabled
           : blink::WebContentLayerClient::GraphicsContextDisabled);