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

chrome/browser/ui/views/tabs/tab.cc

 // 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.
 
 #include "chrome/browser/ui/views/tabs/tab.h"
 
 #include <limits>
 
 #include "base/command_line.h"
 #include "base/debug/alias.h"
@@ skipping 681 matching lines @@
   const bool extend_to_top =
       widget && (widget->IsMaximized() || widget->IsFullscreen());
 
   // Hit mask constants.
   const SkScalar kTabCapWidth = 15;
   const SkScalar kTabTopCurveWidth = 4;
   const SkScalar kTabBottomCurveWidth = 3;
 #if defined(OS_MACOSX)
   // Mac's Cocoa UI doesn't have shadows.
   const SkScalar kTabInset = 0;
-  const SkScalar kTabTop = 0;
 #elif defined(TOOLKIT_VIEWS)
   // The views browser UI has shadows in the left, right and top parts of the
   // tab.
   const SkScalar kTabInset = 6;
-  const SkScalar kTabTop = 2;
 #endif
 
   SkScalar left = kTabInset;
-  SkScalar top = kTabTop;
+  SkScalar top = GetLayoutConstant(TAB_TOP_EXCLUSION_HEIGHT);
   SkScalar right = SkIntToScalar(width()) - kTabInset;
   SkScalar bottom = SkIntToScalar(height());
 
   // Start in the lower-left corner.
   mask->moveTo(left, bottom);
 
   // Left end cap.
   mask->lineTo(left + kTabBottomCurveWidth, bottom - kTabBottomCurveWidth);
   mask->lineTo(left + kTabCapWidth - kTabTopCurveWidth,
                top + kTabTopCurveWidth);
   mask->lineTo(left + kTabCapWidth, top);
 
   // Extend over the top shadow area if we have one and the caller wants it.
-  if (kTabTop > 0 && extend_to_top) {
+  if (top > 0 && extend_to_top) {
     mask->lineTo(left + kTabCapWidth, 0);
     mask->lineTo(right - kTabCapWidth, 0);
   }
 
   // Connect to the right cap.
   mask->lineTo(right - kTabCapWidth, top);
 
   // Right end cap.
   mask->lineTo(right - kTabCapWidth + kTabTopCurveWidth,
                top + kTabTopCurveWidth);
@@ skipping 807 matching lines @@
                          const gfx::ImageSkia& image) {
   DCHECK_NE(scale_factor, ui::SCALE_FACTOR_NONE);
   ImageCacheEntry entry;
   entry.resource_id = resource_id;
   entry.scale_factor = scale_factor;
   entry.image = image;
   image_cache_->push_front(entry);
   if (image_cache_->size() > kMaxImageCacheSize)
     image_cache_->pop_back();
 }