[Mac] Fix tabstrip background opacity problem when dragging tabs.

chrome/browser/ui/cocoa/tabs/tab_window_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_window_controller.h"
 
 #include "base/logging.h"
 #import "base/mac/sdk_forward_declarations.h"
 #import "chrome/browser/ui/cocoa/browser_window_layout.h"
 #import "chrome/browser/ui/cocoa/fast_resize_view.h"
@@ skipping 160 matching lines @@
     // followed by RenderWidgetHost::Blur(), which would result in an unexpected
     // loss of focus.
     focusBeforeOverlay_.reset([[FocusTracker alloc] initWithWindow:window]);
     [window makeFirstResponder:nil];
 
     // Move the original window's tab strip view and content view to the overlay
     // window. The content view is added as a subview of the overlay window's
     // content view (rather than using setContentView:) because the overlay
     // window has a different content size (due to it being borderless).
     [[overlayWindow_ contentView] addSubview:[self tabStripView]];
+    [[self tabStripView] setInATabDraggingOverlayWindow:YES];
     [[overlayWindow_ contentView] addSubview:originalContentView_];
 
     [overlayWindow_ orderFront:nil];
   } else if (!useOverlay && overlayWindow_) {
     DCHECK(originalContentView_);
 
     // Return the original window's tab strip view and content view to their
     // places. The TabStripView always needs to be in front of the window's
     // content view and therefore it should always be added after the content
     // view is set.
     [[window contentView] addSubview:originalContentView_
                           positioned:NSWindowBelow
                           relativeTo:nil];
     originalContentView_.frame = [[window contentView] bounds];
     [[window contentView] addSubview:[self tabStripView]];
+    [[self tabStripView] setInATabDraggingOverlayWindow:NO];
     [[window contentView] updateTrackingAreas];
 
     [focusBeforeOverlay_ restoreFocusInWindow:window];
     focusBeforeOverlay_.reset();
 
     [window display];
     [window removeChildWindow:overlayWindow_];
 
     [overlayWindow_ orderOut:nil];
     [overlayWindow_ release];
@@ skipping 172 matching lines @@
   [visualEffectView addSubview:tabStripBackgroundView_];
 }
 
 // Called when the size of the window content area has changed. Override to
 // position specific views. Base class implementation does nothing.
 - (void)layoutSubviews {
   NOTIMPLEMENTED();
 }
 
 @end