Move BitmapPlatformDevice::makeOpaque into a shared file

skia/ext/bitmap_platform_device_linux.h

Index: skia/ext/bitmap_platform_device_linux.h
diff --git a/skia/ext/bitmap_platform_device_linux.h b/skia/ext/bitmap_platform_device_linux.h
index 172a0f149fb32cf24166b5568c22405f8d8dc657..1c6579cc15fba7358e3c0599057306e09b11753d 100644
--- a/skia/ext/bitmap_platform_device_linux.h
+++ b/skia/ext/bitmap_platform_device_linux.h
@@ -79,6 +79,8 @@ class BitmapPlatformDevice : public PlatformDevice {
   // A stub copy constructor.  Needs to be properly implemented.
   BitmapPlatformDevice(const BitmapPlatformDevice& other);
 
+  virtual void makeOpaque(int x, int y, int width, int height);
+
   // Bitmaps aren't vector graphics.
   virtual bool IsVectorial() { return false; }