Mac: fix Esc-key cancellation of bookmark bar button drags.

chrome/browser/cocoa/bookmark_button.h

Index: chrome/browser/cocoa/bookmark_button.h
diff --git a/chrome/browser/cocoa/bookmark_button.h b/chrome/browser/cocoa/bookmark_button.h
index 79c878a2ca1b4136ac59d1bf6c33a1eead1e2741..ea3decce4c70bd94b43b44d56751d0f20b6342c6 100644
--- a/chrome/browser/cocoa/bookmark_button.h
+++ b/chrome/browser/cocoa/bookmark_button.h
@@ -7,8 +7,9 @@
 // Class for bookmark bar buttons that can be drag sources.
 @interface BookmarkButton : NSButton {
  @private
-  BOOL draggable_;
-  BOOL beingDragged_;  // are we being dragged?
+  BOOL draggable_;     // Is this a draggable type of button?
+  BOOL mayDragStart_;  // Set to YES on mouse down, NO on up or drag.
+  BOOL beingDragged_;
 
   // Initial mouse-down to prevent a hair-trigger drag.
   NSPoint initialMouseDownLocation_;