mac: New asset for the tabstrip border, tweak drawing.

chrome/browser/ui/cocoa/tabs/tab_strip_view.mm

Index: chrome/browser/ui/cocoa/tabs/tab_strip_view.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_strip_view.mm b/chrome/browser/ui/cocoa/tabs/tab_strip_view.mm
index 35d3c091dd0151e93c9a03fedfbe569a39701302..0bc50071b4ace4e379ca0574bfd1ff0753e33245 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_strip_view.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_strip_view.mm
@@ -19,6 +19,10 @@
 #include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 
+// When the window doesn't have focus then we want to draw the button with a
+// slightly lighter color. We do this by just reducing the alpha.
+const CGFloat kImageNoFocusAlpha = 0.65;
+
 @implementation TabStripView
 
 @synthesize dropArrowShown = dropArrowShown_;
@@ -75,8 +79,10 @@
   borderRect.size.height = [image size].height;
   borderRect.origin.y = 0;
 
-  NSDrawThreePartImage(borderRect, nil, image, nil, /*vertical=*/NO,
-                       NSCompositeSourceOver, 1.0, /*flipped=*/NO);
+  bool active = [[self window] isKeyWindow] || [[self window] isMainWindow];
+  NSDrawThreePartImage(borderRect, nil, image, nil, /*vertical=*/ NO,
+                       NSCompositeSourceOver,
+                       active ? 1.0 : kImageNoFocusAlpha, /*flipped=*/ NO);
 }
 
 - (void)drawRect:(NSRect)rect {