CoreAnimation: Reduce VA usage by extra layers

chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.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 "chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.h"
 
 #import "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #import "base/mac/sdk_forward_declarations.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller_target.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_strip_view.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_view.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_window_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_strip_controller.h"
+#include "ui/gfx/mac/scoped_ns_disable_screen_updates.h"
 
 const CGFloat kTearDistance = 36.0;
 const NSTimeInterval kTearDuration = 0.333;
 
 // Returns whether |screenPoint| is inside the bounds of |view|.
 static BOOL PointIsInsideView(NSPoint screenPoint, NSView* view) {
   if ([view window] == nil)
     return NO;
   NSPoint windowPoint = [[view window] convertScreenToBase:screenPoint];
   NSPoint viewPoint = [view convertPoint:windowPoint fromView:nil];
@@ skipping 80 matching lines @@
   // Because we move views between windows, we need to handle the event loop
   // ourselves. Ideally we should use the standard event loop.
   while (1) {
     const NSUInteger mask =
         NSLeftMouseUpMask | NSLeftMouseDraggedMask | NSKeyUpMask;
     theEvent =
         [NSApp nextEventMatchingMask:mask
                            untilDate:[NSDate distantFuture]
                               inMode:NSDefaultRunLoopMode
                              dequeue:YES];
+

[ccameron, 2014/04/19 02:45:29]

The dark background was popping through without this -- it turns out that this
fixes a lot of flickering issues during tab drag.

+    // Ensure that any window changes that happen while handling this event
+    // appear atomically.
+    gfx::ScopedNSDisableScreenUpdates disabler;
+
     NSEventType type = [theEvent type];
     if (type == NSKeyUp) {
       if ([theEvent keyCode] == kVK_Escape) {
         // Cancel the drag and restore the previous state.
         if (draggingWithinTabStrip_) {
           // Simply pretend the tab wasn't dragged (far enough).
           tabWasDragged_ = NO;
         } else {
           [targetController_ removePlaceholder];
           if ([sourceController_ numberOfTabs] < 2) {
@@ skipping 364 matching lines @@
     [[targetController_ window] makeMainWindow];
   } else {
     [dragWindow_ setAlphaValue:0.5];
     [[draggedController_ overlayWindow] setHasShadow:NO];
     [[draggedController_ window] makeMainWindow];
   }
   chromeIsVisible_ = shouldBeVisible;
 }
 
 @end