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

chrome/browser/ui/cocoa/tabs/tab_strip_view.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_view.h"
 
 #include <cmath>  // floor
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
@@ skipping 12 matching lines @@
 #import "ui/base/cocoa/nsgraphics_context_additions.h"
 #import "ui/base/cocoa/nsview_additions.h"
 #include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 
 @implementation TabStripView
 
 @synthesize dropArrowShown = dropArrowShown_;
 @synthesize dropArrowPosition = dropArrowPosition_;
+@synthesize inATabDraggingOverlayWindow = inATabDraggingOverlayWindow_;
 
 - (id)initWithFrame:(NSRect)frame {
   self = [super initWithFrame:frame];
   if (self) {
     newTabButton_.reset([[NewTabButton alloc] initWithFrame:
         NSMakeRect(295, 0, 40, 27)]);
     [newTabButton_ setToolTip:l10n_util::GetNSString(IDS_TOOLTIP_NEW_TAB)];
 
     // Set lastMouseUp_ = -1000.0 so that timestamp-lastMouseUp_ is big unless
     // lastMouseUp_ has been reset.
@@ skipping 68 matching lines @@
 }
 
 - (void)drawRect:(NSRect)dirtyRect {
   const ui::ThemeProvider* themeProvider = [[self window] themeProvider];
   bool hasCustomThemeImage = themeProvider &&
       themeProvider->HasCustomImage(IDR_THEME_FRAME);
   bool isModeMaterial = ui::MaterialDesignController::IsModeMaterial();
   BOOL supportsVibrancy = [self visualEffectView] != nil;
   BOOL isMainWindow = [[self window] isMainWindow];
 
-  if (themeProvider && !hasCustomThemeImage && isModeMaterial) {
+  // If in Material Design mode, decrease the tabstrip background's translucency
+  // by overlaying it with a partially-transparent gray (but only if not themed,
+  // and not being used to drag tabs between browser windows). The gray is
+  // somewhat opaque for Incognito mode, very opaque for non-Incognito mode, and
+  // completely opaque when the window is not active.
+  if (themeProvider && !hasCustomThemeImage && isModeMaterial &&
+      !inATabDraggingOverlayWindow_) {
     NSColor* theColor = nil;
     if (isMainWindow) {
-      // The vibrancy overlay makes the Incognito NSVisualEffectView
-      // somewhat darker, and the non-Incognito NSVisualEffectView much darker.
       if (supportsVibrancy &&
           !themeProvider->HasCustomColor(ThemeProperties::COLOR_FRAME)) {
         theColor = themeProvider->GetNSColor(
             ThemeProperties::COLOR_FRAME_VIBRANCY_OVERLAY);
       } else {
         theColor = themeProvider->GetNSColor(ThemeProperties::COLOR_FRAME);
       }
     } else {
-      // Inactive MD windows always draw a solid color.
       theColor = themeProvider->GetNSColor(
           ThemeProperties::COLOR_FRAME_INACTIVE);
     }
 
     if (theColor) {
       [theColor set];
       NSRectFillUsingOperation(dirtyRect, NSCompositeSourceOver);
     }
   }
 
@@ skipping 264 matching lines @@
   } else {
     [visualEffectView setState:NSVisualEffectStateFollowsWindowActiveState];
   }
 }
 
 - (void)windowDidChangeActive {
   [self setNeedsDisplay:YES];
 }
 
 @end