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

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index 95e8661736683a2bdf401251834991b7d476d2dd..4bb22015fd9db93959a82ec30822fdb73502a725 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -435,7 +435,7 @@ void RenderWidgetHostViewAura::MovePluginWindows(
     gfx::Rect clip = moves[i].clip_rect;
     clip.Offset(moves[i].window_rect.origin());
     clip.Offset(scroll_offset);
-    clip = clip.Intersect(view_port);
+    clip.Intersect(view_port);
     clip.Offset(-moves[i].window_rect.x(), -moves[i].window_rect.y());
     clip.Offset(-scroll_offset.x(), -scroll_offset.y());
     moves[i].clip_rect = clip;
@@ -874,7 +874,7 @@ void RenderWidgetHostViewAura::AcceleratedSurfacePostSubBuffer(
     // Damage may not have been DIP aligned, so inflate damage to compensate
     // for any round-off error.
     rect_to_paint.Inset(-1, -1);
-    rect_to_paint = rect_to_paint.Intersect(window_->bounds());
+    rect_to_paint.Intersect(window_->bounds());
 
     window_->SchedulePaintInRect(rect_to_paint);