[Mac] Prevent constrained windows (sheets) from opening while instant preview...

chrome/browser/cocoa/browser_window_controller.mm

 // Copyright (c) 2010 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/cocoa/browser_window_controller.h"
 
 #include <Carbon/Carbon.h>
 
 #include "app/l10n_util.h"
 #include "app/l10n_util_mac.h"
@@ skipping 426 matching lines @@
 }
 
 - (void)attachConstrainedWindow:(ConstrainedWindowMac*)window {
   [tabStripController_ attachConstrainedWindow:window];
 }
 
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window {
   [tabStripController_ removeConstrainedWindow:window];
 }
 
+- (BOOL)canAttachConstrainedWindow {
+  return ![previewableContentsController_ isShowingPreview];
+}
+
 - (void)updateDevToolsForContents:(TabContents*)contents {
   [devToolsController_ updateDevToolsForTabContents:contents];
   [devToolsController_ ensureContentsVisible];
 }
 
 - (void)updateSidebarForContents:(TabContents*)contents {
   [sidebarController_ updateSidebarForTabContents:contents];
   [sidebarController_ ensureContentsVisible];
 }
 
@@ skipping 1589 matching lines @@
 
 - (BOOL)supportsBookmarkBar {
   return [self supportsWindowFeature:Browser::FEATURE_BOOKMARKBAR];
 }
 
 - (BOOL)isNormalWindow {
   return browser_->type() == Browser::TYPE_NORMAL;
 }
 
 @end  // @implementation BrowserWindowController(WindowType)