Render the tab close button as a vector-based icon.

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

 // 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.
 
 #ifndef CHROME_BROWSER_UI_VIEWS_TABS_TAB_H_
 #define CHROME_BROWSER_UI_VIEWS_TABS_TAB_H_
 
 #include <list>
 #include <string>
 
@@ skipping 261 matching lines @@
 
   void DisplayCrashedFavicon();
   void ResetCrashedFavicon();
 
   void StopCrashAnimation();
   void StartCrashAnimation();
 
   // Returns true if the crash animation is currently running.
   bool IsPerformingCrashAnimation() const;
 
+  // Sets the close button normal-state image using the current
+  // |close_button_color_|.
+  void SetCloseButtonNormalImage();

[miu, 2015/09/18 01:13:37]

naming: When I was originally reading this, I was thinking, "Where's the arg to
this method?"  Suggestions:

  ResetCloseButtonAfterThemeChange();
  DoCloseButtonLayout();
  ...

And wording in the comment should be clarified similarly.

[Peter Kasting, 2015/09/18 01:17:13]

Neither of those names would be accurate, though.  This is not called only after
a theme change, and it does not do any close button layout.  It only sets the
close button's normal image.  I can't think of a more accurate name than the
current one, and it seems like the comment makes clear why there doesn't need to
be an arg.

[miu, 2015/09/19 00:19:58]

It's a moot point now (at patch set 3), but back at patch set 1, it was clearly
meant to be called only after a theme change: The one time it wasn't called for
that reason, you had added a giant comment about why you have to call it without
knowing the correct color.  ;-)

Also, in that giant comment, you said "so that the close button gets sized and
laid out correctly."

Just rationalizing my earlier drive-by suggestions...I'll bow-out now.

+
   // Schedules repaint task for icon.
   void ScheduleIconPaint();
 
   // Returns a |path| containing the region that matches the bitmap display of
   // this tab, for input event hit testing.  Set |include_top_shadow| to include
   // the mostly-transparent shadow pixels above the top edge of the tab in the
   // path.
   void GetHitTestMaskHelper(bool include_top_shadow, gfx::Path* path) const;
 
   // Returns the rectangle for the light bar in immersive mode.
@@ skipping 107 matching lines @@
   SkColor close_button_color_;
 
   // As the majority of the tabs are inactive, and painting tabs is slowish,
   // we cache a handful of the inactive tab backgrounds here.
   static ImageCache* image_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(Tab);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_TABS_TAB_H_