OOPIF: Support session restore by combining/splitting frame PageStates.

content/browser/frame_host/navigation_entry_impl.h

Index: content/browser/frame_host/navigation_entry_impl.h
diff --git a/content/browser/frame_host/navigation_entry_impl.h b/content/browser/frame_host/navigation_entry_impl.h
index 8d97ef39871055859583b4c36a48b7e4d78c0423..c3ccd17537be89383aa18cabe4762f5219508fb4 100644
--- a/content/browser/frame_host/navigation_entry_impl.h
+++ b/content/browser/frame_host/navigation_entry_impl.h
@@ -201,6 +201,11 @@ class CONTENT_EXPORT NavigationEntryImpl
   FrameNavigationEntry* GetFrameEntryByUniqueName(
       const std::string& unique_name) const;
 
+  // In OOPIF modes, this updates the cached copy of the full PageState whenever
+  // a frame's individual state changes. Keeping a cached copy is necessary to
+  // be able to return a const ref from GetPageState.

[Avi (use Gerrit), 2015/12/02 19:17:43]

I would much rather change the API. PageState isn't that big, and if we can
return a copy by value rather than const ref, then we can avoid the error-prone
scheme of having to call UpdatePageState after updating the state of any given
frame and simplify this a lot.

[Charlie Reis, 2015/12/02 19:48:18]

I can give it another try in a preliminary CL, though I remember it quickly got
unwieldy the last time I attempted.

Needing to call UpdatePageState alongside FNE::set_page_state is definitely
unfortunate, but I did kind of like having a separate NavEntry::page_state_ from
FNE::page_state_, since that frees us up to move FNE to a FrameState object
instead (while still supporting default Chrome).

[Charlie Reis, 2015/12/02 20:44:14]

Ah, I was mistaken!  The last time, I tried to remove the const first, hoping to
preserve the const ref (by keeping a cached copy).  Removing the const was the
viral change.

Dropping the const ref is much easier (and leads to a simpler CL).  We can do a
separate PageState for NavigationEntryImpl later when we start to move towards
FrameState.  Thanks for the suggestion!

[Avi (use Gerrit), 2015/12/02 21:15:45]

You're welcome.

Returning a const object by value is weird anyway.

+  void UpdatePageState();
+
   void set_unique_id(int unique_id) {
     unique_id_ = unique_id;
   }
@@ -394,6 +399,12 @@ class CONTENT_EXPORT NavigationEntryImpl
   base::Time timestamp_;
   int http_status_code_;
 
+  // In default Chrome, this is the PageState reported from the renderer. In
+  // OOPIF modes, this is a cached copy of the PageState generated from the
+  // various FrameNavigationEntry states. In either case, it is persisted to
+  // support session/tab restore.
+  PageState page_state_;
+
   // This member is not persisted with session restore because it is transient.
   // If the post request succeeds, this field is cleared since the same
   // information is stored in |content_state_| above. It is also only shallow