Implement webview.captureVisibleRegion()

content/browser/frame_host/render_widget_host_view_child_frame.h

Index: content/browser/frame_host/render_widget_host_view_child_frame.h
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.h b/content/browser/frame_host/render_widget_host_view_child_frame.h
index c77b216b229ced95bdb1745c45adcd44515e7205..817bc2e8f3e6fb481ccce66bd3588ca30fff8e98 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.h
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.h
@@ -8,8 +8,10 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <deque>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "build/build_config.h"
@@ -58,6 +60,15 @@ class CONTENT_EXPORT RenderWidgetHostViewChildFrame
     frame_connector_ = frame_connector;
   }
 
+  // This functions registers single-use callbacks that want to be notified when
+  // the next frame is swapped. The callback is triggered by
+  // OnSwapCompositorFrame, which is the appropriate time to request pixel
+  // readback for the frame that is about to be drawn. Once called, the callback
+  // pointer is released.
+  // TODO(wjmaclean): We should consider making this available in other view
+  // types, such as RenderWidgetHostViewAura.
+  void RegisterFrameSwappedCallback(scoped_ptr<base::Closure> callback);
+
   // RenderWidgetHostView implementation.
   void InitAsChild(gfx::NativeView parent_view) override;
   RenderWidgetHost* GetRenderWidgetHost() const override;
@@ -175,6 +186,8 @@ class CONTENT_EXPORT RenderWidgetHostViewChildFrame
   // Clears current compositor surface, if one is in use.
   void ClearCompositorSurfaceIfNecessary();
 
+  void ProcessFrameSwappedCallbacks();
+
   // The last scroll offset of the view.
   gfx::Vector2dF last_scroll_offset_;
 
@@ -205,6 +218,16 @@ class CONTENT_EXPORT RenderWidgetHostViewChildFrame
   }
 
  private:
+  void SubmitSurfaceCopyRequest(const gfx::Rect& src_subrect,
+                                const gfx::Size& dst_size,
+                                const ReadbackRequestCallback& callback,
+                                const SkColorType preferred_color_type);
+
+  using FrameSwappedCallbackList = std::deque<scoped_ptr<base::Closure>>;
+  // Since frame-drawn callbacks are "fire once", we use std::deque to make
+  // it convenient to swap() when processing the list.
+  FrameSwappedCallbackList frame_swapped_callbacks_;
+
   base::WeakPtrFactory<RenderWidgetHostViewChildFrame> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewChildFrame);
 };