Fix going back to a script-injected about:blank frame.

content/browser/frame_host/navigation_entry_impl.cc

 // Copyright 2013 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.
 
 #include "content/browser/frame_host/navigation_entry_impl.h"
 
 #include <stddef.h>
 
 #include <queue>
 #include <utility>
@@ skipping 854 matching lines @@
   NavigationEntryImpl::TreeNode* tree_node = FindFrameEntry(frame_tree_node);
   return tree_node ? tree_node->frame_entry.get() : nullptr;
 }
 
 std::set<std::string> NavigationEntryImpl::GetSubframeUniqueNames(
     FrameTreeNode* frame_tree_node) const {
   std::set<std::string> names;
   NavigationEntryImpl::TreeNode* tree_node = FindFrameEntry(frame_tree_node);
   if (tree_node) {
     // Return the names of all immediate children.
-    for (TreeNode* child : tree_node->children)
+    for (TreeNode* child : tree_node->children) {
+      // Ignore subframe unique names if we would just be staying at
+      // about:blank, since the renderer should be allowed to just commit the
+      // initial blank frame those cases.  PageState doesn't matter there,
+      // because content injected into about:blank frames doesn't use it.
+      //
+      // Be careful not to include iframe srcdoc URLs, which do need their
+      // PageState.  The committed URL in that case gets rewritten to
+      // about:blank, but we can detect in the PageState's URL.

[alexmos, 2016/10/21 06:34:16]

nit: missing "it" after can detect?

[Charlie Reis, 2016/10/21 07:34:30]

Done.

+      //
+      // See https://crbug.com/657896 for details.
+      // TODO(creis): Find a way to detect cases when the iframe started at a
+      // real URL and later went to about:blank, since those are broken for now.
+      ExplodedPageState exploded_page_state;
+      if (DecodePageState(child->frame_entry->page_state().ToEncodedData(),
+                          &exploded_page_state)) {
+        ExplodedFrameState frame_state = exploded_page_state.top;
+        if (UTF16ToUTF8(frame_state.url_string.string()) == url::kAboutBlankURL)
+          continue;
+      }
+
       names.insert(child->frame_entry->frame_unique_name());
+    }
   }
   return names;
 }
 
 void NavigationEntryImpl::ClearStaleFrameEntriesForNewFrame(
     FrameTreeNode* frame_tree_node) {
   DCHECK(!frame_tree_node->IsMainFrame());
 
   NavigationEntryImpl::TreeNode* node = nullptr;
   std::queue<NavigationEntryImpl::TreeNode*> work_queue;
@@ skipping 51 matching lines @@
       return node;
 
     // Enqueue any children and keep looking.
     for (auto* child : node->children)
       work_queue.push(child);
   }
   return nullptr;
 }
 
 }  // namespace content