Revert of Remove the is_loading_ field from WebContentsImpl

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 c8596d624c00390cd2276405e7f7a1a8e650b9ab..81282c0e9a654fbb9e25c55db3c955bbebe4c87b 100644
--- a/content/browser/frame_host/frame_tree.h
+++ b/content/browser/frame_host/frame_tree.h
@@ -41,7 +41,6 @@
 class CONTENT_EXPORT FrameTree {
  public:
   class NodeRange;
-  class ConstNodeRange;
 
   class CONTENT_EXPORT NodeIterator {
    public:
@@ -76,41 +75,6 @@
 
     FrameTree* const tree_;
     FrameTreeNode* const node_to_skip_;
-  };
-
-  class CONTENT_EXPORT ConstNodeIterator {
-   public:
-    ~ConstNodeIterator();
-
-    ConstNodeIterator& operator++();
-
-    bool operator==(const ConstNodeIterator& rhs) const;
-    bool operator!=(const ConstNodeIterator& rhs) const {
-      return !(*this == rhs);
-    }
-
-    const FrameTreeNode* operator*() { return current_node_; }
-
-   private:
-    friend class ConstNodeRange;
-
-    ConstNodeIterator(const FrameTreeNode* starting_node);
-
-    const FrameTreeNode* current_node_;
-    std::queue<const FrameTreeNode*> queue_;
-  };
-
-  class CONTENT_EXPORT ConstNodeRange {
-   public:
-    ConstNodeIterator begin();
-    ConstNodeIterator end();
-
-   private:
-    friend class FrameTree;
-
-    ConstNodeRange(const FrameTree* tree);
-
-    const FrameTree* const tree_;
   };
 
   // Each FrameTreeNode will default to using the given |navigator| for
@@ -145,10 +109,6 @@
   // breadth-first traversal order.
   NodeRange Nodes();
 
-  // Returns a range to iterate over all FrameTreeNodes in the frame tree in
-  // breadth-first traversal order. All FrameTreeNodes returned will be const.
-  ConstNodeRange ConstNodes() const;
-
   // Adds a new child frame to the frame tree. |process_id| is required to
   // disambiguate |new_routing_id|, and it must match the process of the
   // |parent| node. Otherwise no child is added and this method returns false.
@@ -227,7 +187,7 @@
   void ResetLoadProgress();
 
   // Returns true if at least one of the nodes in this FrameTree is loading.
-  bool IsLoading() const;
+  bool IsLoading();
 
   // Set page-level focus in all SiteInstances involved in rendering
   // this FrameTree, not including the current main frame's