Mac: Fix incorrect tab dragging window drawing.

chrome/browser/ui/cocoa/background_gradient_view.mm

Index: chrome/browser/ui/cocoa/background_gradient_view.mm
diff --git a/chrome/browser/ui/cocoa/background_gradient_view.mm b/chrome/browser/ui/cocoa/background_gradient_view.mm
index fdad7a826f4d3a4cfbdcf6a863d2908f3f3d1efc..df151d2aa6075db3fba07dd80ab4f6bdee3316c4 100644
--- a/chrome/browser/ui/cocoa/background_gradient_view.mm
+++ b/chrome/browser/ui/cocoa/background_gradient_view.mm
@@ -115,8 +115,9 @@
   [super viewDidMoveToWindow];
   if ([self window]) {
     // The new window for the view may have a different focus state than the
-    // last window this view was part of. Force a re-draw to ensure that the
-    // view draws the right state.
+    // last window this view was part of.
+    // This happens when the view is moved into a TabWindowOverlayWindow for
+    // tab dragging.
     [self windowDidChangeActive];
   }
 }