Implement "Look Up In Dictionary" context menu item asynchronously.

content/browser/renderer_host/render_widget_host_view_mac.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.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
 
@@ skipping 2337 matching lines @@
 
 - (void)smartMagnifyWithEvent:(NSEvent*)event {
   const WebGestureEvent& smartMagnifyEvent =
       WebInputEventFactory::gestureEvent(event, self);
   if (renderWidgetHostView_ && renderWidgetHostView_->render_widget_host_) {
     renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(
         smartMagnifyEvent);
   }
 }
 
-// This is invoked only on 10.8 or newer when the user taps a word using
-// three fingers.
-- (void)quickLookWithEvent:(NSEvent*)event {
-  NSPoint point = [self convertPoint:[event locationInWindow] fromView:nil];
+- (void)showLookUpDictionaryOverlayAtPoint:(NSPoint)point {
+  // The PDF plugin does not support getting the attributed string at point.
+  // TODO: support GetStringAtPoint() for PDF. See crbug.com/152438.
   TextInputClientMac::GetInstance()->GetStringAtPoint(
       renderWidgetHostView_->render_widget_host_,
       gfx::Point(point.x, NSHeight([self frame]) - point.y),
       ^(NSAttributedString* string, NSPoint baselinePoint) {
           if (string && [string length] > 0) {
             dispatch_async(dispatch_get_main_queue(), ^{
                 [self showDefinitionForAttributedString:string
                                                 atPoint:baselinePoint];
             });
           }
       }
   );
 }
 
+// This is invoked only on 10.8 or newer when the user taps a word using
+// three fingers.
+- (void)quickLookWithEvent:(NSEvent*)event {
+  NSPoint point = [self convertPoint:[event locationInWindow] fromView:nil];
+  [self showLookUpDictionaryOverlayAtPoint:point];
+}
+
 // This method handles 2 different types of hardware events.
 // (Apple does not distinguish between them).
 //  a. Scrolling the middle wheel of a mouse.
 //  b. Swiping on the track pad.
 //
 // This method is responsible for 2 types of behavior:
 //  a. Scrolling the content of window.
 //  b. Navigating forwards/backwards in history.
 //
 // This is a brief description of the logic:
@@ skipping 937 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end