Distill the concept of the "tab top exclusion region", an area inside the tab

chrome/browser/ui/views/frame/opaque_browser_frame_view_layout.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/ui/views/frame/opaque_browser_frame_view_layout.h"
 
 #include "base/command_line.h"
 #include "chrome/browser/profiles/profiles_state.h"
 #include "chrome/browser/ui/views/layout_constants.h"
 #include "chrome/browser/ui/views/profiles/avatar_menu_button.h"
 #include "chrome/common/chrome_switches.h"
 #include "components/signin/core/common/profile_management_switches.h"
 #include "ui/gfx/font.h"
 #include "ui/views/controls/button/image_button.h"
 #include "ui/views/controls/label.h"
 
 #if defined(ENABLE_SUPERVISED_USERS)
 #include "chrome/browser/ui/views/profiles/supervised_user_avatar_label.h"
 #endif
 
 namespace {
 
-// Besides the frame border, there's another 9 px of empty space atop the
-// window in restored mode, to use to drag the window around.
-const int kNonClientRestoredExtraThickness = 9;
+// Besides the frame border, there's empty space atop the window in restored
+// mode, to use to drag the window around.
+const int kNonClientRestoredExtraThickness = 11;
 
 // The titlebar never shrinks too short to show the caption button plus some
 // padding below it.
 const int kCaptionButtonHeightWithPadding = 19;
 
 // There is a 5 px gap between the title text and the caption buttons.
 const int kTitleLogoSpacing = 5;
 
 // The frame border is only visible in restored mode and is hardcoded to 4 px on
 // each side regardless of the system window border size.
@@ skipping 184 matching lines @@
   }
 
   int thickness = FrameBorderThickness(restored);
   if (!restored && delegate_->IsTabStripVisible() && IsTitleBarCondensed())
     thickness -= kTabstripTopShadowThickness;
   return thickness;
 }
 
 int OpaqueBrowserFrameViewLayout::GetTabStripInsetsTop(bool restored) const {
   const int top = NonClientTopBorderHeight(restored);
+  // Annoyingly, the pre-MD layout uses different heights for the hit-test
+  // exclusion region (which we want here, since we're trying to size the border
+  // so that the region above the tab's hit-test zone matches) versus the shadow
+  // thickness.
+  const int exclusion = GetLayoutConstant(TAB_TOP_EXCLUSION_HEIGHT);
   return (!restored && (IsTitleBarCondensed() || delegate_->IsFullscreen())) ?
-      top : (top + kNonClientRestoredExtraThickness);
+      top : (top + kNonClientRestoredExtraThickness - exclusion);
 }
 
 int OpaqueBrowserFrameViewLayout::TitlebarBottomThickness(bool restored) const {
   const int edge = kTitlebarTopAndBottomEdgeThickness;
   return (!restored && IsTitleBarCondensed()) ?
       edge : (edge + views::NonClientFrameView::kClientEdgeThickness);
 }
 
 int OpaqueBrowserFrameViewLayout::CaptionButtonY(bool restored) const {
   // Maximized buttons start at window top, since the window has no border. This
@@ skipping 461 matching lines @@
 
 void OpaqueBrowserFrameViewLayout::ViewAdded(views::View* host,
                                              views::View* view) {
   SetView(view->id(), view);
 }
 
 void OpaqueBrowserFrameViewLayout::ViewRemoved(views::View* host,
                                                views::View* view) {
   SetView(view->id(), nullptr);
 }