Fix set_area sizes for RequestCopyOfOutput, and related tests.

NOTE: This is a revival/continuation of https://codereview.chromium.org/333723004, which was started by another developer.

The cc:CopyOutputRequest object assumes the src_subrect region is
in DIP space.  Thus, all calling code should provide the same.

Fixed tests in render_widget_host_view_browsertest.cc that were
completing successfully, even though the implementation was broken
for the high DPI scenarios.

In addition, I updated a number of interface comments to clarify the
difference between src_subrect being in DIP coordinates versus the
dest_size being in physical pixel coordinates.

Dependent on: https://codereview.chromium.org/311253004 (landed at r276139)

BUG=397708,399349

Review URL: https://codereview.chromium.org/462173002

Cr-Commit-Position: refs/heads/master@{#289509}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289509 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/compositor/delegated_frame_host.cc

@@ -183,9 +183,7 @@ void DelegatedFrameHost::CopyFromCompositingSurfaceToVideoFrame(
           subscriber_texture,
           target,
           callback));
-  gfx::Rect src_subrect_in_pixel =
-      ConvertRectToPixel(client_->CurrentDeviceScaleFactor(), src_subrect);
-  request->set_area(src_subrect_in_pixel);
+  request->set_area(src_subrect);
   if (subscriber_texture.get()) {
     request->SetTextureMailbox(
         cc::TextureMailbox(subscriber_texture->mailbox(),

content/browser/media/capture/desktop_capture_device_aura.cc

@@ -278,10 +278,8 @@ void DesktopVideoCaptureMachine::Capture(bool dirty) {
         cc::CopyOutputRequest::CreateRequest(
             base::Bind(&DesktopVideoCaptureMachine::DidCopyOutput,
                        AsWeakPtr(), frame, start_time, capture_frame_cb));
-    gfx::Rect window_rect =
-        ui::ConvertRectToPixel(desktop_window_->layer(),
-                               gfx::Rect(desktop_window_->bounds().width(),
-                                         desktop_window_->bounds().height()));
+    gfx::Rect window_rect = gfx::Rect(desktop_window_->bounds().width(),
+                                      desktop_window_->bounds().height());
     request->set_area(window_rect);
     desktop_window_->layer()->RequestCopyOfOutput(request.Pass());
   }

content/browser/renderer_host/render_widget_host_view_base.h

@@ -243,27 +243,27 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView,
   // Notifies the view that the scroll offset has changed.
   virtual void ScrollOffsetChanged() = 0;
 
-  // Copies the contents of the compositing surface into the given
-  // (uninitialized) PlatformCanvas if any.
-  // The rectangle region specified with |src_subrect| is copied from the
-  // contents, scaled to |dst_size|, and written to |output|.
-  // |callback| is invoked with true on success, false otherwise. |output| can
-  // be initialized even on failure.
-  // A smaller region than |src_subrect| may be copied if the underlying surface
-  // is smaller than |src_subrect|.
-  // NOTE: |callback| is called asynchronously.
+  // Copies the contents of the compositing surface, providing a new SkBitmap
+  // result via an asynchronously-run |callback|. |src_subrect| is specified in
+  // layer space coordinates for the current platform (e.g., DIP for Aura/Mac,
+  // physical for Android), and is the region to be copied from this view. The
+  // copy is then scaled to a SkBitmap of size |dst_size|. |callback| is run
+  // with true on success, false otherwise. A smaller region than |src_subrect|
+  // may be copied if the underlying surface is smaller than |src_subrect|.
   virtual void CopyFromCompositingSurface(
       const gfx::Rect& src_subrect,
       const gfx::Size& dst_size,
       const base::Callback<void(bool, const SkBitmap&)>& callback,
       const SkColorType color_type) = 0;
 
-  // Copies a given subset of the compositing surface's content into a YV12
-  // VideoFrame, and invokes a callback with a success/fail parameter. |target|
-  // must contain an allocated, YV12 video frame of the intended size. If the
-  // copy rectangle does not match |target|'s size, the copied content will be
-  // scaled and letterboxed with black borders. The copy will happen
-  // asynchronously. This operation will fail if there is no available
+  // Copies the contents of the compositing surface, populating the given
+  // |target| with YV12 image data. |src_subrect| is specified in layer space
+  // coordinates for the current platform (e.g., DIP for Aura/Mac, physical for
+  // Android), and is the region to be copied from this view. The copy is then
+  // scaled and letterboxed with black borders to fit |target|. Finally,
+  // |callback| is asynchronously run with true/false for
+  // success/failure. |target| must point to an allocated, YV12 video frame of
+  // the intended size. This operation will fail if there is no available
   // compositing surface.
   virtual void CopyFromCompositingSurfaceToVideoFrame(
       const gfx::Rect& src_subrect,

ui/snapshot/snapshot.h

@@ -41,10 +41,12 @@ SNAPSHOT_EXPORT bool GrabViewSnapshot(
     std::vector<unsigned char>* png_representation,
     const gfx::Rect& snapshot_bounds);
 
+
+// These functions take a snapshot of |source_rect|, specified in layer space
+// coordinates (DIP for desktop, physical pixels for Android), and scale the
+// snapshot to |target_size| (in physical pixels), asynchronously.
 typedef base::Callback<void(const gfx::Image& snapshot)>
     GrabWindowSnapshotAsyncCallback;
-// GrabWindowSnapshotAndScaleAsync() copies snapshot of |source_rect| from
-// window and scales it to |target_size| asynchronously.
 SNAPSHOT_EXPORT void GrabWindowSnapshotAndScaleAsync(
     gfx::NativeWindow window,
     const gfx::Rect& source_rect,