[MacViews] Position modal sheets using ModalDialogHost.

ui/views/widget/native_widget_mac.mm

 // Copyright 2014 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 "ui/views/widget/native_widget_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_nsobject.h"
@@ skipping 87 matching lines @@
   // is still a valid pointer, then reset it.
   if (bridge_) {
     delegate_->OnNativeWidgetDestroying();
     bridge_.reset();
   }
   delegate_->OnNativeWidgetDestroyed();
   if (ownership_ == Widget::InitParams::NATIVE_WIDGET_OWNS_WIDGET)
     delete this;
 }
 
+int NativeWidgetMac::SheetPositionY() {
+  NSView* view = GetNativeView();
+  return
+      [view convertPoint:NSMakePoint(0, NSHeight([view frame])) toView:nil].y;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // NativeWidgetMac, internal::NativeWidgetPrivate implementation:
 
 void NativeWidgetMac::InitNativeWidget(const Widget::InitParams& params) {
   ownership_ = params.ownership;
   base::scoped_nsobject<NSWindow> window([CreateNSWindow(params) retain]);
   [window setReleasedWhenClosed:NO];  // Owned by scoped_nsobject.
   bridge_->Init(window, params);
 
   // Only set always-on-top here if it is true since setting it may affect how
@@ skipping 588 matching lines @@
   [[ViewsNSWindowCloseAnimator alloc] initWithWindow:window];
 }
 
 - (void)animationDidEnd:(NSAnimation*)animation {
   [window_ close];
   [animation_ setDelegate:nil];
   [self release];
 }
 
 @end