[Mac][Material Design] Improve bookmark folder menu performance.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm

 // 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.
 
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.h"
 
 #include <stddef.h>
 
 #include "base/mac/bundle_locations.h"
 #include "base/mac/sdk_forward_declarations.h"
@@ skipping 1355 matching lines @@
   return [[self folderTarget] pasteboardItemForDragOfButton:button];
 }
 
 - (void)willBeginPasteboardDrag {
   // Close our folder menu and submenus since we know we're going to be dragged.
   [self closeBookmarkFolder:self];
 }
 
 // Called from BookmarkButton.
 // Unlike bookmark_bar_controller's version, we DO default to being enabled.
-- (void)mouseEnteredButton:(id)sender event:(NSEvent*)event {
+- (void)mouseEnteredButton:(BookmarkButton*)button event:(NSEvent*)event {
   // Prevent unnecessary button selection change while scrolling due to the
   // size changing that happens in -performOneScroll:.
   if (isScrolling_)
     return;
 
   [[NSCursor arrowCursor] set];
 
-  buttonThatMouseIsIn_ = sender;
-  [self setSelectedButtonByIndex:[self indexOfButton:sender]];
+  // Make sure the mouse is still within the button's bounds (it might not be if
+  // the mouse is moving quickly). Skip this check if |event| is nil (as
+  // documented in the header).
+  if (event && ![[button cell] isMouseReallyInside]) {
+    [NSObject cancelPreviousPerformRequestsWithTarget:self];
+    return;
+  }
+
+  buttonThatMouseIsIn_ = button;
+  [self setSelectedButtonByIndex:[self indexOfButton:button]];
 
   // Cancel a previous hover if needed.
   [NSObject cancelPreviousPerformRequestsWithTarget:self];
 
   // If already opened, then we exited but re-entered the button
   // (without entering another button open), do nothing.
-  if ([folderController_ parentButton] == sender)
+  if ([folderController_ parentButton] == button)
     return;
 
   // If right click was done immediately on entering a button, then open the
   // folder without delay so that context menu appears over the folder menu.
   if ([event type] == NSRightMouseDown)
-    [self openBookmarkFolderFromButtonAndCloseOldOne:sender];
+    [self openBookmarkFolderFromButtonAndCloseOldOne:button];
   else
     [self performSelector:@selector(openBookmarkFolderFromButtonAndCloseOldOne:)
-               withObject:sender
+               withObject:button
                afterDelay:bookmarks::kHoverOpenDelay
                   inModes:[NSArray arrayWithObject:NSRunLoopCommonModes]];
 }
 
 // Called from the BookmarkButton
-- (void)mouseExitedButton:(id)sender event:(NSEvent*)event {
-  if (buttonThatMouseIsIn_ == sender)
+- (void)mouseExitedButton:(BookmarkButton*)button event:(NSEvent*)event {
+  if (buttonThatMouseIsIn_ == button) {
     buttonThatMouseIsIn_ = nil;
     [self setSelectedButtonByIndex:-1];
+  }
 
   // During scrolling -mouseExitedButton: stops scrolling, so update the
   // corresponding status field to reflect is has stopped.
   isScrolling_ = NO;
 
   // Stop any timer about opening a new hover-open folder.
 
   // Since a performSelector:withDelay: on self retains self, it is
   // possible that a cancelPreviousPerformRequestsWithTarget: reduces
   // the refcount to 0, releasing us.  That's a bad thing to do while
@@ skipping 659 matching lines @@
 
 - (void)setIgnoreAnimations:(BOOL)ignore {
   ignoreAnimations_ = ignore;
 }
 
 - (BookmarkButton*)buttonThatMouseIsIn {
   return buttonThatMouseIsIn_;
 }
 
 @end  // BookmarkBarFolderController