Make gfx::Rect class operations consistently mutate the class they are called on.

webkit/plugins/ppapi/ppapi_plugin_instance.cc

Index: webkit/plugins/ppapi/ppapi_plugin_instance.cc
diff --git a/webkit/plugins/ppapi/ppapi_plugin_instance.cc b/webkit/plugins/ppapi/ppapi_plugin_instance.cc
index 0452e855e57f948a43de77a8b90572e671ad27a5..aa9b264f7ab3a5e21c0185e1467b65ac315cb521 100644
--- a/webkit/plugins/ppapi/ppapi_plugin_instance.cc
+++ b/webkit/plugins/ppapi/ppapi_plugin_instance.cc
@@ -1065,11 +1065,14 @@ bool PluginInstance::GetBitmapForOptimizedPluginPaint(
   gfx::Rect pixel_plugin_backing_store_rect(
       0, 0, image_data->width(), image_data->height());
   float scale = GetBoundGraphics2D()->GetScale();
+  gfx::RectF scaled_backing_store_rect = pixel_plugin_backing_store_rect;
+  scaled_backing_store_rect.Scale(scale);
   gfx::Rect plugin_backing_store_rect =
-    gfx::ToEnclosedRect(pixel_plugin_backing_store_rect.Scale(scale));
+    gfx::ToEnclosedRect(scaled_backing_store_rect);
 
   gfx::Rect clip_page = PP_ToGfxRect(view_data_.clip_rect);
-  gfx::Rect plugin_paint_rect = plugin_backing_store_rect.Intersect(clip_page);
+  gfx::Rect plugin_paint_rect = plugin_backing_store_rect;
+  plugin_paint_rect.Intersect(clip_page);
   if (!plugin_paint_rect.Contains(relative_paint_bounds))
     return false;