Plumb physical backing size from RWHV to renderer CC.

This patch introduces a concept of "physical backing size" which is plumbed
down from port-specific browser code to the renderer compositor.

This is distinct from the usual concept of view size on high-DPI screens
with >1 dpi scale.  Physical backing size represents the size of the
texture CC draws to, whereas the view size is given to WebKit and
specifies the CSS width/height.

Before this patch, physical backing size was recalculated in the
renderer by multiplying the view size by DPI scale.  There are two problems
with this:

- This introduces off-by-one errors when DPI scale is non-integral.
  Values such as 1.5 and 1.33125 are common on Android devices.
- The Android port would like to more efficiently implement features like
  on-screen-keyboard bringup and URL-bar hiding without needing to
  resize the backing texture. Separating the value given to CC and to
  WebKit is the first step towards this.

WebKit counterpart at https://bugs.webkit.org/show_bug.cgi?id=110727

NOTRY=true
BUG=152502

Review URL: https://chromiumcodereview.appspot.com/12328080

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185621 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 3 insertions, 0 deletions

diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index 52699be..05470af 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -229,6 +229,9 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView,
 
   virtual void GetScreenInfo(WebKit::WebScreenInfo* results) = 0;
 
+  // The size of the view's backing surface in non-DPI-adjusted pixels.
+  virtual gfx::Size GetPhysicalBackingSize() const = 0;
+
   // Gets the bounds of the window, in screen coordinates.
   virtual gfx::Rect GetBoundsInRootWindow() = 0;