Bug 759653: Use RGB24 for offscreen surfaces on android-esque platforms. r=mwu

gfx/thebes/gfxAndroidPlatform.cpp

@@ -35,7 +35,7 @@ gfxAndroidPlatform::gfxAndroidPlatform()
 
     mOffscreenFormat = mScreenDepth == 16
                        ? gfxASurface::ImageFormatRGB16_565
-                       : gfxASurface::ImageFormatARGB32;
+                       : gfxASurface::ImageFormatRGB24;
 }
 
 gfxAndroidPlatform::~gfxAndroidPlatform()