[Mac] Don't ignore mouse events outside of the view while dragging.

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 <QuartzCore/QuartzCore.h>
 
 #include "base/basictypes.h"
@@ skipping 2080 matching lines @@
   NSView* view = [contentView hitTest:[theEvent locationInWindow]];
   // Traverse the superview hierarchy as the hitTest will return the frontmost
   // view, such as an NSTextView, while nonWebContentView may be specified by
   // its parent view.
   while (view) {
     if ([view respondsToSelector:nonWebContentViewSelector] &&
         [view performSelector:nonWebContentViewSelector]) {
       // The cursor is over a nonWebContentView - ignore this mouse event.
       return YES;
     }
-    if ([view isKindOfClass:[self class]] && ![view isEqual:self]) {
+    if ([view isKindOfClass:[self class]] && ![view isEqual:self] &&
+        !hasOpenMouseDown_) {
       // The cursor is over an overlapping render widget. This check is done by
       // both views so the one that's returned by -hitTest: will end up
       // processing the event.
+      // Note that while dragging, we only get events for the render view where
+      // drag started, even if mouse is  actually over another view or outside
+      // the window. Cocoa does this for us. We should handle these events and
+      // not ignore (since there is no other render view to handle them). Thus
+      // the |!hasOpenMouseDown_| check above.
       return YES;
     }
     view = [view superview];
   }
   return NO;
 }
 
 - (void)mouseEvent:(NSEvent*)theEvent {
   TRACE_EVENT0("browser", "RenderWidgetHostViewCocoa::mouseEvent");
   if (delegate_ && [delegate_ respondsToSelector:@selector(handleEvent:)]) {
@@ skipping 1810 matching lines @@
   return YES;
 }
 
 - (BOOL)isOpaque {
   if (renderWidgetHostView_->use_core_animation_)
     return YES;
   return [super isOpaque];
 }
 
 @end