Move BitmapPlatformDevice::makeOpaque into a shared file

skia/ext/platform_device_mac.h

Index: skia/ext/platform_device_mac.h
diff --git a/skia/ext/platform_device_mac.h b/skia/ext/platform_device_mac.h
index a32667f43d3497a5aedaef03b7adf9debca1a5d0..258e44894f5f85721759bab20433ea4c8312d4db 100644
--- a/skia/ext/platform_device_mac.h
+++ b/skia/ext/platform_device_mac.h
@@ -60,18 +60,6 @@ class PlatformDevice : public SkDevice {
   // Loads the specified Skia transform into the device context
   static void LoadTransformToCGContext(CGContextRef context,
                                        const SkMatrix& matrix);
-
-  // Function pointer used by the processPixels method for setting the alpha
-  // value of a particular pixel.
-  typedef void (*adjustAlpha)(uint32_t* pixel);
-
-  // Loops through each of the pixels in the specified range, invoking
-  // adjustor for the alpha value of each pixel.
-  virtual void processPixels(int x,
-                             int y,
-                             int width,
-                             int height,
-                             adjustAlpha adjustor) = 0;
 };
 
 }  // namespace skia