add peekPixels to canvas

include/core/SkDevice.h

Index: include/core/SkDevice.h
diff --git a/include/core/SkDevice.h b/include/core/SkDevice.h
index 016e2babc88d9048255a9f90174e4a159f0bee9c..0653d7146388836a6df3ef36ecf5b24a217d6592 100644
--- a/include/core/SkDevice.h
+++ b/include/core/SkDevice.h
@@ -77,6 +77,13 @@ public:
     }
 
     /**
+     *  Return ImageInfo for this device. If the canvas is not backed by pixels
+     *  (cpu or gpu), then the info's ColorType will be kUnknown_SkColorType.
+     */
+    virtual SkImageInfo imageInfo() const;
+    
+
+    /**
      *  Return the bounds of the device in the coordinate space of the root
      *  canvas. The root device will have its top-left at 0,0, but other devices
      *  such as those associated with saveLayer may have a non-zero origin.
@@ -369,7 +376,10 @@ protected:
 protected:
     // default impl returns NULL
     virtual SkSurface* newSurface(const SkImageInfo&);
-
+    
+    // default impl returns NULL
+    virtual const void* peekPixels(SkImageInfo*, size_t* rowBytes);
+    
     /**
      *  Leaky properties are those which the device should be applying but it isn't.
      *  These properties will be applied by the draw, when and as it can.