This patch adds NextSibling() to FrameTreeNode.

content/browser/frame_host/frame_tree_unittest.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.h"
 
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "content/browser/frame_host/navigator_impl.h"
 #include "content/browser/frame_host/render_frame_host_factory.h"
@@ skipping 282 matching lines @@
   EXPECT_EQ(nullptr, frame_tree->FindByRoutingID(process_id, 37));
 
   // Ensure they can be found by name, if they have one.
   EXPECT_EQ(root, frame_tree->FindByName(std::string()));
   EXPECT_EQ(child0, frame_tree->FindByName("child0"));
   EXPECT_EQ(child1, frame_tree->FindByName("child1"));
   EXPECT_EQ(grandchild, frame_tree->FindByName("grandchild"));
   EXPECT_EQ(nullptr, frame_tree->FindByName("no such frame"));
 }
 
-// Check that PreviousSibling() is retrieved correctly.
-TEST_F(FrameTreeTest, PreviousSibling) {
+// Check that PreviousSibling() and NextSibling() are retrieved correctly.
+TEST_F(FrameTreeTest, GetSibling) {
   main_test_rfh()->InitializeRenderFrameIfNeeded();
 
   // Add a few child frames to the main frame.
   FrameTree* frame_tree = contents()->GetFrameTree();
   FrameTreeNode* root = frame_tree->root();
   main_test_rfh()->OnCreateChildFrame(22, blink::WebTreeScopeType::Document,
                                       "child0", blink::WebSandboxFlags::None,
                                       blink::WebFrameOwnerProperties());
   main_test_rfh()->OnCreateChildFrame(23, blink::WebTreeScopeType::Document,
                                       "child1", blink::WebSandboxFlags::None,
                                       blink::WebFrameOwnerProperties());
   main_test_rfh()->OnCreateChildFrame(24, blink::WebTreeScopeType::Document,
                                       "child2", blink::WebSandboxFlags::None,
                                       blink::WebFrameOwnerProperties());
   FrameTreeNode* child0 = root->child_at(0);
   FrameTreeNode* child1 = root->child_at(1);
   FrameTreeNode* child2 = root->child_at(2);
 
   // Add one grandchild frame.
   child1->current_frame_host()->OnCreateChildFrame(
       33, blink::WebTreeScopeType::Document, "grandchild",
       blink::WebSandboxFlags::None, blink::WebFrameOwnerProperties());
   FrameTreeNode* grandchild = child1->child_at(0);
 
+  // Test PreviousSibling().
   EXPECT_EQ(nullptr, root->PreviousSibling());
   EXPECT_EQ(nullptr, child0->PreviousSibling());
   EXPECT_EQ(child0, child1->PreviousSibling());
   EXPECT_EQ(child1, child2->PreviousSibling());
   EXPECT_EQ(nullptr, grandchild->PreviousSibling());
+
+  // Test NextSibling().
+  EXPECT_EQ(nullptr, root->NextSibling());
+  EXPECT_EQ(child1, child0->NextSibling());
+  EXPECT_EQ(child2, child1->NextSibling());
+  EXPECT_EQ(nullptr, child2->NextSibling());
+  EXPECT_EQ(nullptr, grandchild->NextSibling());
 }
 
 // Do some simple manipulations of the frame tree, making sure that
 // WebContentsObservers see a consistent view of the tree as we go.
 TEST_F(FrameTreeTest, ObserverWalksTreeDuringFrameCreation) {
   TreeWalkingWebContentsLogger activity(contents());
   contents()->NavigateAndCommit(GURL("http://www.google.com"));
   EXPECT_EQ("RenderFrameCreated(2) -> 2: []", activity.GetLog());
 
   FrameTree* frame_tree = contents()->GetFrameTree();
@@ skipping 107 matching lines @@
   // Crash the renderer.
   main_test_rfh()->GetProcess()->SimulateCrash();
 
   // Ensure they cannot be found by id after the process has crashed.
   EXPECT_FALSE(FrameTreeNode::GloballyFindByID(id1));
   EXPECT_FALSE(FrameTreeNode::GloballyFindByID(id2));
   EXPECT_FALSE(FrameTreeNode::GloballyFindByID(id3));
 }
 
 }  // namespace content