Make RenderFrameHostManager swap RenderFrameHosts, not RenderViewHosts.

content/browser/frame_host/frame_tree.h

Index: content/browser/frame_host/frame_tree.h
diff --git a/content/browser/frame_host/frame_tree.h b/content/browser/frame_host/frame_tree.h
index 3ef2d4c979e4550c28f48ce51d48f57f7d379174..b49bf3bc477e4d77c7975b853d70ce428471506e 100644
--- a/content/browser/frame_host/frame_tree.h
+++ b/content/browser/frame_host/frame_tree.h
@@ -53,6 +53,8 @@ class CONTENT_EXPORT FrameTree {
             RenderFrameHostManager::Delegate* manager_delegate);
   ~FrameTree();
 
+  FrameTreeNode* root() const { return root_.get(); }
+
   // Returns the FrameTreeNode with the given |frame_tree_node_id|.
   FrameTreeNode* FindByID(int64 frame_tree_node_id);
 
@@ -83,18 +85,12 @@ class CONTENT_EXPORT FrameTree {
                    int64 frame_id);
   void SetFrameUrl(int64 frame_id, const GURL& url);
 
-  // Resets the FrameTree and changes RenderFrameHost for the main frame.
+  // Clears process specific-state after a main frame process swap.
   // This destroys most of the frame tree but retains the root node so that
   // navigation state may be kept on it between process swaps. Used to
   // support bookkeeping for top-level navigations.
-  //
-  // If |main_frame| is NULL, reset tree to initially constructed state.
-  //
-  // TODO(ajwong): This function should not be given a |main_frame|. This is
-  // required currently because the RenderViewHost owns its main frame. When
-  // that relation is fixed, the FrameTree should be responsible for
-  // created/destroying the main frame on the swap.
-  void SwapMainFrame(RenderFrameHostImpl* main_frame);
+  // TODO(creis): Look into how we can remove the need for this method.
+  void ResetForMainFrameSwap();
 
   // Convenience accessor for the main frame's RenderFrameHostImpl.
   RenderFrameHostImpl* GetMainFrame() const;
@@ -106,9 +102,25 @@ class CONTENT_EXPORT FrameTree {
   void SetFrameRemoveListener(
       const base::Callback<void(RenderViewHostImpl*, int64)>& on_frame_removed);
 
-  FrameTreeNode* root() const { return root_.get(); }
+  // Gets the RenderViewHost needed for a new RenderFrameHost in the given
+  // |site_instance|, creating it if necessary.  The RenderViewHost will have
+  // its Shutdown method called when all of the RenderFrameHosts using it are
+  // deleted.
+  RenderViewHostImpl* GetRenderViewHostForNewFrame(SiteInstance* site_instance,
+                                                   int routing_id,
+                                                   int main_frame_routing_id,
+                                                   bool swapped_out,
+                                                   bool hidden);
+
+  // Keeps track of which RenderFrameHosts are using each RenderViewHost.  When
+  // the number drops to zero, we call Shutdown on the RenderViewHost.
+  void RegisterRenderFrameHost(RenderFrameHostImpl* render_frame_host);
+  void UnregisterRenderFrameHost(RenderFrameHostImpl* render_frame_host);
 
  private:
+  typedef std::pair<RenderViewHostImpl*, int> RenderViewHostRefCount;
+  typedef base::hash_map<int, RenderViewHostRefCount> RenderViewHostMap;
+
   // Returns the FrameTreeNode with the given renderer-specific |frame_id|.
   // For internal use only.
   // TODO(creis): Replace this with a version that takes in a routing ID.
@@ -116,8 +128,7 @@ class CONTENT_EXPORT FrameTree {
 
   scoped_ptr<FrameTreeNode> CreateNode(int64 frame_id,
                                        const std::string& frame_name,
-                                       int render_frame_host_id,
-                                       FrameTreeNode* parent_node);
+                                       Navigator* navigator);
 
   // These delegates are installed into all the RenderViewHosts and
   // RenderFrameHosts that we create.
@@ -126,6 +137,15 @@ class CONTENT_EXPORT FrameTree {
   RenderWidgetHostDelegate* render_widget_delegate_;
   RenderFrameHostManager::Delegate* manager_delegate_;
 
+  // Map of SiteInstance ID to a (RenderViewHost, refcount) pair.  This allows
+  // us to look up the RenderViewHost for a given SiteInstance when creating
+  // RenderFrameHosts, and it allows us to call Shutdown on the RenderViewHost
+  // and remove it from the map when no more RenderFrameHosts are using it.
+  //
+  // Must be declared before |root_| so that it is deleted afterward.  Otherwise
+  // the map will be cleared before we delete the RenderFrameHosts in the tree.
+  RenderViewHostMap render_view_host_map_;
+
   scoped_ptr<FrameTreeNode> root_;
 
   base::Callback<void(RenderViewHostImpl*, int64)> on_frame_removed_;