mac: Fix flickering of install extension window.

chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.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/constrained_window/constrained_window_custom_sheet.h"
 
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller.h"
 #import "ui/base/cocoa/constrained_window/constrained_window_animation.h"
 
 // Length of the animation in seconds.
 const NSTimeInterval kAnimationDuration = 0.18;
 
 @implementation CustomConstrainedWindowSheet
 
 - (id)initWithCustomWindow:(NSWindow*)customWindow {
   if ((self = [super init])) {
     customWindow_.reset([customWindow retain]);
   }
   return self;
 }
 
 - (void)setUseSimpleAnimations:(BOOL)simpleAnimations {
   useSimpleAnimations_ = simpleAnimations;
 }
 
 - (void)showSheetForWindow:(NSWindow*)window {
   base::scoped_nsobject<NSAnimation> animation;
-  if (!useSimpleAnimations_) {
+  if (useSimpleAnimations_) {
+    [customWindow_ setAlphaValue:0.0];
+  } else {
     animation.reset(
         [[ConstrainedWindowAnimationShow alloc] initWithWindow:customWindow_]);
   }
   [window addChildWindow:customWindow_
                  ordered:NSWindowAbove];
   [self unhideSheet];
   [self updateSheetPosition];
   [customWindow_ makeKeyAndOrderFront:nil];
 
   if (useSimpleAnimations_) {
-    [customWindow_ setAlphaValue:0.0];
     [NSAnimationContext beginGrouping];
     [[NSAnimationContext currentContext] setDuration:kAnimationDuration];
     [[customWindow_ animator] setAlphaValue:1.0];
     [NSAnimationContext endGrouping];
   } else {
     [animation startAnimation];
   }
 }
 
 - (void)closeSheetWithAnimation:(BOOL)withAnimation {
@@ skipping 57 matching lines @@
 
 - (void)resizeWithNewSize:(NSSize)size {
   // NOOP
 }
 
 - (NSWindow*)sheetWindow {
   return customWindow_;
 }
 
 @end