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

content/browser/frame_host/frame_tree_unittest.cc

Index: content/browser/frame_host/frame_tree_unittest.cc
diff --git a/content/browser/frame_host/frame_tree_unittest.cc b/content/browser/frame_host/frame_tree_unittest.cc
index d1ec9a7f7e710c43cbda144f6e678fdb27c3d918..417b34862bb3bf3770e1433e588fdcc1f4a95da4 100644
--- a/content/browser/frame_host/frame_tree_unittest.cc
+++ b/content/browser/frame_host/frame_tree_unittest.cc
@@ -244,6 +244,30 @@
   EXPECT_EQ(nullptr, frame_tree->FindByName("no such frame"));
 }
 
+// Check that PreviousSibling() is retrieved correctly.
+TEST_F(FrameTreeTest, PreviousSibling) {
+  // Add a few child frames to the main frame.
+  FrameTree* frame_tree = contents()->GetFrameTree();
+  FrameTreeNode* root = frame_tree->root();
+  main_test_rfh()->OnCreateChildFrame(22, "child0", SandboxFlags::NONE);
+  main_test_rfh()->OnCreateChildFrame(23, "child1", SandboxFlags::NONE);
+  main_test_rfh()->OnCreateChildFrame(24, "child2", SandboxFlags::NONE);
+  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, "grandchild",
+                                                   SandboxFlags::NONE);
+  FrameTreeNode* grandchild = child1->child_at(0);
+
+  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());
+}
+
 // 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) {