Move unique name generation and tracking into //content.

content/renderer/unique_name_helper.h

Index: content/renderer/unique_name_helper.h
diff --git a/content/renderer/unique_name_helper.h b/content/renderer/unique_name_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..96ed7cd01a39386434458f6bc67509dba5bf9ccc
--- /dev/null
+++ b/content/renderer/unique_name_helper.h
@@ -0,0 +1,114 @@
+// 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.
+
+#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;
+
+// Frame helper that manages the details of generating a quasi-stable unique
+// name for the frame. The name is unique within a page, and is used for:
+// - matching up session history items with recreated frames
+// - layout test results
+//
+// 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).

[Charlie Reis, 2017/03/20 20:11:39]

minor nit: Can you fix the indent here?  I'm not picky on what you use (since
the groups don't seem to agree on whether to align with each other or their
respective ::=='s), but lines 40-41 should at least agree with each other.  :)

[dcheng, 2017/03/21 22:03:41]

Done.

+//
+//   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
+
+class UniqueNameHelper {
+ public:
+  explicit UniqueNameHelper(RenderFrameImpl* render_frame);
+  ~UniqueNameHelper();
+
+  // Returns the generated unique name.
+  const std::string& value() const { return unique_name_; }
+
+  // Used to propagate an already calculated unique name.
+  //
+  // TODO(lukasza): It would be nice to assert uniqueness of the propagated
+  // name here but:
+  // 1) uniqueness is currently violated by provisional/old frame pairs.
+  // 2) there is an unresolved race between 2 OOPIFs, that can result in a
+  //    non-unique unique name: see https://crbug.com/558680#c14.
+  void set_propagated_name(const std::string& name) { unique_name_ = name; }
+
+  // Note: when creating a new child frame, the unique name needs to be
+  // calculated before the RenderFrameImpl is created. To avoid this chicken and
+  // egg problem, this method is static, which means that |parent| needs to be
+  // passed as a parameter.
+  static std::string GenerateNameForNewChildFrame(blink::WebFrame* parent,
+                                                  const std::string& name);

[Charlie Reis, 2017/03/20 20:11:39]

Please also document what we're expecting about |name|.  If I understand
correctly, it's supposed to be the assigned name of the frame, or if that's
empty, then the fallback name.  Is that right?  (That's what
FrameTree::calculateUniqueNameForChildFrame used to do internally, which we
don't do here.  Looks like it's done at the call site in
RenderFrameImpl::createChildFrame instead.)

[dcheng, 2017/03/21 22:03:42]

I've documented this centrally in RenderFrameImpl. UniqueNameHelper itself
doesn't really care what the inputs are, and this documents the subtlety where
it happens.

+
+  // 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_