Move unique name generation and tracking into //content.

content/renderer/unique_name_helper.h

+// Copyright 2017 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.
+//
+// Description of the current unique name format
+// ---------------------------------------------
+//
+// Changing the format of unique name is undesirable, because it breaks
+// backcompatibility of session history (which stores unique names
+// generated in the past on user's disk).  This incremental,
+// backcompatibility-aware approach has resulted so far in the following
+// rather baroque format... :
+//
+//   uniqueName ::= <nullForMainFrame> | <assignedName> | <generatedName>
+//                 (generatedName is used if assignedName is
+//                 non-unique / conflicts with other frame's unique name.
+//
+//   assignedName ::= value of iframe's name attribute
+//                 or value assigned to window.name (*before* the first
+//                    real commit - afterwards unique name stays immutable).
+//
+//   generatedName ::= oldGeneratedName newUniqueSuffix?
+//                  (newUniqueSuffix is only present if oldGeneratedName was
+//                  not unique after all)
+//
+//   oldGeneratedName ::= "<!--framePath //" ancestorChain
+//                        "/<!--frame" childCount "-->-->"
+//                  (oldGeneratedName is generated by
+//                  generateUniqueNameCandidate method).
+//
+//   childCount ::= current number of siblings
+//
+//   ancestorChain ::= concatenated unique names of ancestor chain,
+//                     terminated on the first ancestor (if any) starting with
+//                     "<!--framePath"; each ancestor's unique name is
+//                     separated by "/" character
+//   ancestorChain example1: "grandparent/parent"
+//  (ancestor's unique names :   #1--^   | #2-^ )
+//   ancestorChain example2:
+//                     "<!--framePath //foo/bar/<!--frame42-->-->/blah/foobar"
+//  (ancestor's unique names:
+//                              ^--#1--^                         | #2 | #3-^ )
+//
+//   newUniqueSuffix ::= "<!--framePosition" framePosition "/" retryNumber
+//                       "-->"
+//
+//   framePosition ::= "-" numberOfSiblingsBeforeChild
+//                     [ framePosition-forParent? ]
+//
+//   retryNumber ::= smallest non-negative integer resulting in unique name
+
+#ifndef CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_
+#define CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_
+
+#include <string>
+
+#include "base/macros.h"
+
+namespace blink {
+class WebFrame;
+class WebLocalFrame;
+}  // namespace blink
+
+namespace content {
+
+class RenderFrameImpl;
+
+class UniqueNameHelper {

[Charlie Reis, 2017/03/02 23:59:18]

Let's add a class level comment.  Something like:

Manages the complexity in generating a unique name for a frame, which is used to
match up session history items with corresponding frames.

(I would also suggest moving the large explanation comment from above to be just
below this description.)

[dcheng, 2017/03/03 10:22:08]

Done: I merged the comment documenting value() into here, to avoid too much
redundancy.

+ public:
+  explicit UniqueNameHelper(RenderFrameImpl* render_frame);
+  ~UniqueNameHelper();
+
+  const std::string& value() const { return unique_name_; }
+
+  // Used to propagate an already calculated unique name.
+  void set_propagated_name(const std::string& name) { unique_name_ = name; }
+
+  // Note: |parent| needs to be plumbed in for new child frames, since the
+  // unique name needs to be calculated before the new child RenderFrameImpl is
+  // created.
+  static std::string GenerateNameForNewChildFrame(blink::WebFrame* parent,

[Charlie Reis, 2017/03/02 23:59:18]

Why does this need to be static?  Looks like it's only called from
createChildFrame.  (Mainly surprising, not necessarily a problem.  If it's
useful to do so, let's say why in the comment.)

[dcheng, 2017/03/03 10:22:08]

There's a chicken and egg problem here. We need to calculate the unique name for
a child frame that does not yet exist. To avoid having a UniqueNameHelper
instance have to deal with two subtly different codepaths, I've merged them into
one by plumbing in the correct parent to be using.

+                                                  const std::string& name);
+
+  // Called after a browsing context name change to generate a new name. Note
+  // that this should not be called if the frame is no longer displaying the
+  // initial empty document, as unique name changes after that point will break
+  // history navigations. See https://crbug.com/607205.
+  void UpdateName(const std::string& name);
+
+ private:
+  blink::WebLocalFrame* GetWebFrame() const;
+
+  RenderFrameImpl* const render_frame_;
+  std::string unique_name_;
+
+  DISALLOW_COPY_AND_ASSIGN(UniqueNameHelper);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_