Fix the problem that notifications and panels overlap.

chrome/browser/notifications/balloon_collection_impl.h

Index: chrome/browser/notifications/balloon_collection_impl.h
diff --git a/chrome/browser/notifications/balloon_collection_impl.h b/chrome/browser/notifications/balloon_collection_impl.h
index 887d1f27ddd615d645b2cecad7817039fea837b5..c242a69327dadf3f627456594eb127982a0102df 100644
--- a/chrome/browser/notifications/balloon_collection_impl.h
+++ b/chrome/browser/notifications/balloon_collection_impl.h
@@ -16,6 +16,8 @@
 #include "base/message_loop.h"
 #include "chrome/browser/notifications/balloon_collection.h"
 #include "chrome/browser/notifications/balloon_collection_base.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
 
@@ -32,7 +34,8 @@
 // shown on the screen.  It positions new notifications according to
 // a layout, and monitors for balloons being closed, which it reports
 // up to its parent, the notification UI manager.
-class BalloonCollectionImpl : public BalloonCollection
+class BalloonCollectionImpl : public BalloonCollection,
+                              public content::NotificationObserver
 #if USE_OFFSETS
                             , public MessageLoopForUI::Observer
 #endif
@@ -54,6 +57,11 @@ class BalloonCollectionImpl : public BalloonCollection
   virtual void OnBalloonClosed(Balloon* source);
   virtual const Balloons& GetActiveBalloons();
 
+  // content::NotificationObserver interface.
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
   // MessageLoopForUI::Observer interface.
 #if defined(OS_WIN) || defined(TOUCH_UI) || defined(USE_AURA)
   virtual base::EventStatus WillProcessEvent(
@@ -133,6 +141,8 @@ class BalloonCollectionImpl : public BalloonCollection
     int HorizontalEdgeMargin() const;
     int InterBalloonMargin() const;
 
+    void ComputeOffsetsToMoveAbovePanels();
+
     // Minimum and maximum size of balloon content.
     static const int kBalloonMinWidth = 300;
     static const int kBalloonMaxWidth = 300;
@@ -141,6 +151,13 @@ class BalloonCollectionImpl : public BalloonCollection
 
     Placement placement_;
     gfx::Rect work_area_;
+
+    // The offsets that guarantees that the notificaitons shown in the
+    // bottom-right or bottom-left corner of the screen will go above currently
+    // shown panels and will not be obscured by them.
+    int bottom_left_offset_to_move_above_panels_;
+    int bottom_right_offset_to_move_above_panels_;
+
     DISALLOW_COPY_AND_ASSIGN(Layout);
   };
 
@@ -171,6 +188,8 @@ class BalloonCollectionImpl : public BalloonCollection
   // The layout parameters for balloons in this collection.
   Layout layout_;
 
+  content::NotificationRegistrar registrar_;
+
 #if USE_OFFSETS
   // Start and stop observing all UI events.
   void AddMessageLoopObserver();