Specify fullscreen ppapi root layer bounds in pixels

Note from the comments in cc::Layer that the bounds of root cc::Layers
are specified in pixels, in contrast with those of non-root cc::Layers,
which are specified in DIPs.

Add a compositor_viewport_pixel_size() accessor to RenderWidget to
access this from the sub-class (naming is due the pending renaming of
physical_backing_size to compositor_viewport_pixel_size).

Bug: 814690
Change-Id: Ia8033961e04f18c374123b4f9f8da96be131edc7
Reviewed-on: https://chromium-review.googlesource.com/954359Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541923}

content/renderer/render_widget.h

@@ -190,6 +190,9 @@ class CONTENT_EXPORT RenderWidget
   blink::WebInputMethodController* GetInputMethodController() const;
 
   const gfx::Size& size() const { return size_; }
+  const gfx::Size& compositor_viewport_pixel_size() const {
+    return physical_backing_size_;
+  }
   bool is_fullscreen_granted() const { return is_fullscreen_granted_; }
   blink::WebDisplayMode display_mode() const { return display_mode_; }
   bool is_hidden() const { return is_hidden_; }

content/renderer/render_widget_fullscreen_pepper.cc

@@ -337,7 +337,9 @@ void RenderWidgetFullscreenPepper::SetLayer(blink::WebLayer* layer) {
   }
   if (!compositor())
     InitializeLayerTreeView();
-  layer_->SetBounds(blink::WebSize(size()));
+  // Note that root cc::Layers' bounds are specified in pixels (in contrast with
+  // non-root cc::Layers' bounds, which are specified in DIPs).
+  layer_->SetBounds(blink::WebSize(compositor_viewport_pixel_size()));
   layer_->SetDrawsContent(true);
   compositor_->SetRootLayer(*layer_);
 }
@@ -375,8 +377,10 @@ void RenderWidgetFullscreenPepper::Close() {
 }
 
 void RenderWidgetFullscreenPepper::OnResize(const ResizeParams& params) {
+  // Note that root cc::Layers' bounds are specified in pixels (in contrast with
+  // non-root cc::Layers' bounds, which are specified in DIPs).
   if (layer_)
-    layer_->SetBounds(blink::WebSize(params.new_size));
+    layer_->SetBounds(blink::WebSize(params.physical_backing_size));
   RenderWidget::OnResize(params);
 }