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

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

Index: chrome/browser/ui/views/tabs/tab.h
diff --git a/chrome/browser/ui/views/tabs/tab.h b/chrome/browser/ui/views/tabs/tab.h
index c489362579855c14b2e33e36d4b943fcfe84cc55..d5f9b75ffd49cd7aa2f3fc93bfe0a3c30c1e013d 100644
--- a/chrome/browser/ui/views/tabs/tab.h
+++ b/chrome/browser/ui/views/tabs/tab.h
@@ -279,6 +279,10 @@ class Tab : public gfx::AnimationDelegate,
   // 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();