Fix use-after-free when navigating a subframe to about:blank.

content/browser/site_per_process_browsertest.cc

Index: content/browser/site_per_process_browsertest.cc
diff --git a/content/browser/site_per_process_browsertest.cc b/content/browser/site_per_process_browsertest.cc
index c91e6b1592c5ed9150be7eb3b562882b55a28d60..6f112e56b5c581c31a86a66de9e0342f3ac6a557 100644
--- a/content/browser/site_per_process_browsertest.cc
+++ b/content/browser/site_per_process_browsertest.cc
@@ -4739,6 +4739,37 @@ IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest,
   EXPECT_EQ(1, child_count);
 }
 
+// Similar to NavigateProxyAndDetachBeforeCommit, but uses a synchronous
+// navigation to about:blank and the parent removes the child frame in a load
+// event handler for the subframe.
+IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest, NavigateAboutBlankAndDetach) {
+  GURL main_url(
+      embedded_test_server()->GetURL("a.com", "/remove_frame_on_load.html"));
+  EXPECT_TRUE(NavigateToURL(shell(), main_url));
+
+  WebContents* contents = shell()->web_contents();
+  FrameTreeNode* root =
+      static_cast<WebContentsImpl*>(contents)->GetFrameTree()->root();
+  EXPECT_EQ(1U, root->child_count());
+  FrameTreeNode* child = root->child_at(0);
+  EXPECT_NE(shell()->web_contents()->GetSiteInstance(),
+            child->current_frame_host()->GetSiteInstance());
+
+  // Navigate the child frame to "about:blank" from the parent document.
+  TestNavigationObserver observer(shell()->web_contents());
+  EXPECT_TRUE(
+      ExecuteScript(root->current_frame_host(),

[dcheng, 2016/03/03 18:24:16]

I was going to suggest that this test could be written entirely in JS… but I
guess that would make the synchronization harder. So this seems fine.

+                    base::StringPrintf("f.src = '%s'", url::kAboutBlankURL)));
+  observer.Wait();
+
+  // Make sure the a.com renderer does not crash and the frame is removed.
+  int child_count = 0;
+  EXPECT_TRUE(ExecuteScriptAndExtractInt(
+      root->current_frame_host(), "domAutomationController.send(frames.length)",
+      &child_count));
+  EXPECT_EQ(0, child_count);
+}
+
 // Test for https://crbug.com/568670.  In A-embed-B, simultaneously have B
 // create a new (local) child frame, and have A detach B's proxy.  The child
 // frame creation sends an IPC to create a new proxy in A's process, and if