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

webkit/tools/test_shell/webwidget_host_win.cc

Index: webkit/tools/test_shell/webwidget_host_win.cc
diff --git a/webkit/tools/test_shell/webwidget_host_win.cc b/webkit/tools/test_shell/webwidget_host_win.cc
index db5244ad3bc8dc41b2305060d8f4e619a015ccda..75fd90c85d2cd7b7ada728e4ad0adb0c41effff4 100644
--- a/webkit/tools/test_shell/webwidget_host_win.cc
+++ b/webkit/tools/test_shell/webwidget_host_win.cc
@@ -249,7 +249,7 @@ void WebWidgetHost::Paint() {
   webwidget_->layout();
 
   // Scroll the canvas if necessary
-  scroll_rect_ = client_rect.Intersect(scroll_rect_);
+  scroll_rect_.Intersect(client_rect);
   if (!scroll_rect_.IsEmpty()) {
     skia::ScopedPlatformPaint scoped_platform_paint(canvas_.get());
     HDC hdc = scoped_platform_paint.GetPlatformSurface();
@@ -265,7 +265,7 @@ void WebWidgetHost::Paint() {
   // first time we call it.  This is necessary because some WebCore rendering
   // objects update their layout only when painted.
   for (int i = 0; i < 2; ++i) {
-    paint_rect_ = client_rect.Intersect(paint_rect_);
+    paint_rect_.Intersect(client_rect);
     if (!paint_rect_.IsEmpty()) {
       gfx::Rect rect(paint_rect_);
       paint_rect_ = gfx::Rect();