Fix the problem that notifications and panels overlap.

chrome/browser/notifications/balloon_collection_mac.mm

 // Copyright (c) 2009 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 "chrome/browser/notifications/balloon_collection_impl.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "chrome/browser/ui/cocoa/notifications/balloon_view_bridge.h"
 
@@ skipping 17 matching lines @@
 }
 
 int BalloonCollectionImpl::Layout::HorizontalEdgeMargin() const {
   return 5;
 }
 
 int BalloonCollectionImpl::Layout::VerticalEdgeMargin() const {
   return 0;
 }
 
+bool BalloonCollectionImpl::Layout::NeedToMoveAboveLeftSidePanels() const {
+  return placement_ == VERTICALLY_FROM_TOP_LEFT;
+}
+
+bool BalloonCollectionImpl::Layout::NeedToMoveAboveRightSidePanels() const {
+  return placement_ == VERTICALLY_FROM_TOP_RIGHT;
+}
+
 void BalloonCollectionImpl::PositionBalloons(bool reposition) {
   // Use an animation context so that all the balloons animate together.
   [NSAnimationContext beginGrouping];
   [[NSAnimationContext currentContext] setDuration:0.1f];
   PositionBalloonsInternal(reposition);
   [NSAnimationContext endGrouping];
 }
 
 void BalloonCollectionImpl::SetPositionPreference(
     PositionPreference position) {
   if (position == DEFAULT_POSITION)
     position = UPPER_RIGHT;
 
   // All positioning schemes are vertical, but mac
   // uses a vertically reversed screen orientation.
   if (position == UPPER_RIGHT)
     layout_.set_placement(Layout::VERTICALLY_FROM_BOTTOM_RIGHT);
   else if (position == UPPER_LEFT)
     layout_.set_placement(Layout::VERTICALLY_FROM_BOTTOM_LEFT);
   else if (position == LOWER_LEFT)
     layout_.set_placement(Layout::VERTICALLY_FROM_TOP_LEFT);
   else if (position == LOWER_RIGHT)
     layout_.set_placement(Layout::VERTICALLY_FROM_TOP_RIGHT);
   else
     NOTREACHED();
 
+  layout_.ComputeOffsetToMoveAbovePanels(gfx::Rect());
   PositionBalloons(true);
 }
 
 // static
 BalloonCollection* BalloonCollection::Create() {
   return new BalloonCollectionImpl();
 }