Revert of Revert of OOPIF: Specify previous sibling frames when creating new RenderFrames.

content/browser/frame_host/frame_tree_node.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/frame_tree_node.h"
 
 #include <queue>
 
 #include "base/command_line.h"
 #include "base/profiler/scoped_tracker.h"
@@ skipping 141 matching lines @@
     return false;
 
   for (FrameTreeNode* node = parent(); node; node = node->parent()) {
     if (node == other)
       return true;
   }
 
   return false;
 }
 
+FrameTreeNode* FrameTreeNode::PreviousSibling() const {
+  if (!parent_)
+    return nullptr;
+
+  for (size_t i = 0; i < parent_->child_count(); ++i) {
+    if (parent_->child_at(i) == this)
+      return (i == 0) ? nullptr : parent_->child_at(i - 1);
+  }
+
+  NOTREACHED() << "FrameTreeNode not found in its parent's children.";
+  return nullptr;
+}
+
 bool FrameTreeNode::IsLoading() const {
   RenderFrameHostImpl* current_frame_host =
       render_manager_.current_frame_host();
   RenderFrameHostImpl* pending_frame_host =
       render_manager_.pending_frame_host();
 
   DCHECK(current_frame_host);
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnableBrowserSideNavigation)) {
@@ skipping 111 matching lines @@
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "465796 FrameTreeNode::DidStopLoading::End"));
 }
 
 void FrameTreeNode::DidChangeLoadProgress(double load_progress) {
   loading_progress_ = load_progress;
   frame_tree_->UpdateLoadProgress();
 }
 
 }  // namespace content