prerender: Preserve browsing history upon activation.

In the multi-WebContents implementation, history must be copied from
the old WebContents's NavigationController.

Also adjust a unittest to more fully simulate navigation, as it's
necessary to commit the navigation in order to copy the history.

Bug: 1132746
Change-Id: I0e2061451779d1fa9e4db2957aa06d0a05bef436
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2612291Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841405}

content/browser/prerender/prerender_browsertest.cc

@@ -386,6 +386,30 @@ IN_PROC_BROWSER_TEST_P(PrerenderBrowserTest, Activation_PopUpWindow) {
   EXPECT_EQ(GetRequestCount(kPrerenderingUrl), 2);
 }
 
+// Tests that back-forward history is preserved after activation.
+IN_PROC_BROWSER_TEST_P(PrerenderBrowserTest, HistoryAfterActivation) {
+  // This test is only meaningful with activation.
+  if (IsActivationDisabled())
+    return;
+
+  const GURL kInitialUrl = GetUrl("/prerender/add_prerender.html");
+  const GURL kPrerenderingUrl = GetUrl("/empty.html");
+
+  // Navigate to an initial page.
+  ASSERT_TRUE(NavigateToURL(shell(), kInitialUrl));
+
+  // Make and activate a prerendered page.
+  AddPrerender(kPrerenderingUrl);
+  NavigateWithLocation(kPrerenderingUrl);
+  EXPECT_EQ(shell()->web_contents()->GetLastCommittedURL(), kPrerenderingUrl);
+
+  // Navigate back to the initial page.
+  content::TestNavigationObserver observer(shell()->web_contents());
+  shell()->GoBackOrForward(-1);
+  observer.Wait();
+  EXPECT_EQ(shell()->web_contents()->GetLastCommittedURL(), kInitialUrl);
+}
+
 // TODO(https://crbug.com/1132746): Test canceling prerendering.
 
 // TODO(https://crbug.com/1132746): Test prerendering for 404 page, redirection,

content/browser/prerender/prerender_host.cc

@@ -82,6 +82,10 @@ bool PrerenderHost::ActivatePrerenderedContents(
   if (!current_web_contents)
     return false;
 
+  // Merge browsing history.
+  prerendered_contents_->GetController().CopyStateFromAndPrune(
+      &current_web_contents->GetController(), /*replace_entry=*/false);
+
   // Activate the prerendered contents.
   WebContentsDelegate* delegate = current_web_contents->GetDelegate();
   DCHECK(delegate);

content/browser/prerender/prerender_host.h

@@ -47,7 +47,8 @@ class CONTENT_EXPORT PrerenderHost final : public WebContentsObserver {
 
   // Activates the prerendered contents. Returns false when activation didn't
   // occur for some reason. This must be called after this host gets ready for
-  // activation.
+  // activation. `current_render_frame_host` is the RenderFrameHost that will
+  // be swapped out and destroyed by the activation.
   bool ActivatePrerenderedContents(
       RenderFrameHostImpl& current_render_frame_host);
 

content/browser/prerender/prerender_host_unittest.cc

@@ -6,6 +6,7 @@
 
 #include "base/test/scoped_feature_list.h"
 #include "content/browser/site_instance_impl.h"
+#include "content/public/test/navigation_simulator.h"
 #include "content/public/test/test_browser_context.h"
 #include "content/test/test_render_frame_host.h"
 #include "content/test/test_render_view_host.h"
@@ -54,7 +55,7 @@ class PrerenderHostTest : public RenderViewHostImplTestHarness {
   std::unique_ptr<TestWebContentsDelegate> web_contents_delegate_;
 };
 
-TEST_F(PrerenderHostTest, StartPrerendering) {
+TEST_F(PrerenderHostTest, PrerenderAndActivate) {
   std::unique_ptr<TestWebContents> web_contents =
       CreateWebContents(GURL("https://example.com/"));
   RenderFrameHostImpl* initiator_rfh = web_contents->GetMainFrame();
@@ -67,17 +68,25 @@ TEST_F(PrerenderHostTest, StartPrerendering) {
       std::move(attributes), initiator_rfh->GetGlobalFrameRoutingId(),
       initiator_rfh->GetLastCommittedOrigin());
 
+  // Start the prerendering navigation.
   prerender_host->StartPrerendering();
-  // Prepare a fake response so as to commit the navigation.
-  TestRenderFrameHost* prerendering_rfh = static_cast<TestRenderFrameHost*>(
-      prerender_host->GetPrerenderedMainFrameHostForTesting());
-  ASSERT_TRUE(prerendering_rfh);
-  prerendering_rfh->PrepareForCommit();
-
-  // Artificially finish navigation to make the prerender host ready to provide
-  // the prerendered contents.
-  prerender_host->DidFinishNavigation(nullptr);
 
+  // Finish the prerendering navigation. Normally we could use
+  // EmbeddedTestServer to provide a response, but this test uses
+  // RenderViewHostImplTestHarness so the load goes through a
+  // TestNavigationURLLoader which we don't have access to in order
+  // to complete. Use NavigationSimulator to finish the navigation on the
+  // WebContents.
+  WebContents* prerender_contents = WebContents::FromRenderFrameHost(
+      prerender_host->GetPrerenderedMainFrameHostForTesting());
+  ASSERT_TRUE(prerender_contents);
+  std::unique_ptr<NavigationSimulator> sim =
+      NavigationSimulator::CreateFromPending(prerender_contents);
+  sim->ReadyToCommit();
+  sim->Commit();
+  EXPECT_TRUE(prerender_host->is_ready_for_activation());
+
+  // Activate.
   EXPECT_TRUE(prerender_host->ActivatePrerenderedContents(*initiator_rfh));
 }