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

webkit/tools/test_shell/webwidget_host_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <Cocoa/Cocoa.h>
 
 #include "webkit/tools/test_shell/webwidget_host.h"
 
 #include "base/logging.h"
 #include "skia/ext/platform_canvas.h"
@@ skipping 79 matching lines @@
 }
 
 void WebWidgetHost::DidInvalidateRect(const gfx::Rect& damaged_rect) {
 #ifndef NDEBUG
   DLOG_IF(WARNING, painting_) << "unexpected invalidation while painting";
 #endif
 
   // If this invalidate overlaps with a pending scroll, then we have to
   // downgrade to invalidating the scroll rect.
   if (damaged_rect.Intersects(scroll_rect_)) {
-    paint_rect_ = paint_rect_.Union(scroll_rect_);
+    paint_rect_.Union(scroll_rect_);
     ResetScrollRect();
   }
-  paint_rect_ = paint_rect_.Union(damaged_rect);
+  paint_rect_.Union(damaged_rect);
 
   NSRect r = NSRectFromCGRect(damaged_rect.ToCGRect());
   // flip to cocoa coordinates
   r.origin.y = [view_ frame].size.height - r.size.height - r.origin.y;
   [view_ setNeedsDisplayInRect:r];
 }
 
 void WebWidgetHost::DidScrollRect(int dx, int dy, const gfx::Rect& clip_rect) {
   DCHECK(dx || dy);
 
   // If we already have a pending scroll operation or if this scroll operation
   // intersects the existing paint region, then just failover to invalidating.
   if (!scroll_rect_.IsEmpty() || paint_rect_.Intersects(clip_rect)) {
-    paint_rect_ = paint_rect_.Union(scroll_rect_);
+    paint_rect_.Union(scroll_rect_);
     ResetScrollRect();
-    paint_rect_ = paint_rect_.Union(clip_rect);
+    paint_rect_.Union(clip_rect);
   }
 
   // We will perform scrolling lazily, when requested to actually paint.
   scroll_rect_ = clip_rect;
   scroll_dx_ = dx;
   scroll_dy_ = dy;
 
   NSRect r = NSRectFromCGRect(clip_rect.ToCGRect());
   // flip to cocoa coordinates
   r.origin.y = [view_ frame].size.height - r.size.height - r.origin.y;
@@ skipping 24 matching lines @@
   set_painting(false);
 }
 
 WebWidgetHost::~WebWidgetHost() {
   // ui::SetWindowUserData(hwnd_, 0);
 
   webwidget_->close();
 }
 
 void WebWidgetHost::UpdatePaintRect(const gfx::Rect& rect) {
-  paint_rect_ = paint_rect_.Union(rect);
+  paint_rect_.Union(rect);
 }
 
 void WebWidgetHost::Paint() {
   gfx::Rect client_rect(NSRectToCGRect([view_ frame]));
   NSGraphicsContext* view_context = [NSGraphicsContext currentContext];
   CGContextRef context = static_cast<CGContextRef>([view_context graphicsPort]);
 
   // Allocate a canvas if necessary
   if (!canvas_.get()) {
     ResetScrollRect();
     paint_rect_ = client_rect;
     canvas_.reset(new skia::PlatformCanvas(
         paint_rect_.width(), paint_rect_.height(), true));
   }
 
   // make sure webkit draws into our bitmap, not the window
   CGContextRef bitmap_context =
       skia::GetBitmapContext(skia::GetTopDevice(*canvas_));
   [NSGraphicsContext setCurrentContext:
       [NSGraphicsContext graphicsContextWithGraphicsPort:bitmap_context
                                                  flipped:YES]];
 
   webwidget_->animate(0.0);
 
   // This may result in more invalidation
   webwidget_->layout();
 
   // Scroll the canvas if necessary
-  scroll_rect_ = client_rect.Intersect(scroll_rect_);
+  scroll_rect_.Intersect(client_rect);
   if (!scroll_rect_.IsEmpty()) {
     // add to invalidate rect, since there's no equivalent of ScrollDC.
-    paint_rect_ = paint_rect_.Union(scroll_rect_);
+    paint_rect_.Union(scroll_rect_);
   }
   ResetScrollRect();
 
   // Paint the canvas if necessary.  Allow painting to generate extra rects the
   // 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();
 
 //      DLOG_IF(WARNING, i == 1) << "painting caused additional invalidations";
       PaintRect(rect);
     }
   }
   DCHECK(paint_rect_.IsEmpty());
 
@@ skipping 62 matching lines @@
 void WebWidgetHost::PaintRect(const gfx::Rect& rect) {
 #ifndef NDEBUG
   DCHECK(!painting_);
 #endif
   DCHECK(canvas_.get());
 
   set_painting(true);
   webwidget_->paint(webkit_glue::ToWebCanvas(canvas_.get()), rect);
   set_painting(false);
 }