Suppress NEW_NAVIGATION_ENTRY prerenderer failures for ORIGIN_OFFLINE

We have noticed some FINAL_STATUS_NEW_NAVIGATION_ENTRY failures in UMA
for offline pages but didn't know how to trigger them. Bug 675767 has
identified a site (foxsports.com) with articles/links that do have this
issue. The issue is repeatable for those pages and they are never
succeeding. I end-to-end tested this change with logging to confirm
we do repeatably see entry count going to 2 and that with this change
the pages can background load successfully.

BUG=675767

Review-Url: https://codereview.chromium.org/2656653002
Cr-Commit-Position: refs/heads/master@{#446379}

chrome/browser/prerender/prerender_browsertest.cc

@@ -3110,6 +3110,31 @@ IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, PrerenderNewNavigationEntry) {
                    FINAL_STATUS_NEW_NAVIGATION_ENTRY, 1);
 }
 
+// Checks that the prerendering of a page for ORIGIN_OFFLINE is not canceled
+// when the prerendered page tries to make a second navigation entry.
+IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest,
+                       PrerenderNewNavigationEntryForOffline) {
+  // Navigate to about:blank to get the session storage namespace.
+  ui_test_utils::NavigateToURL(current_browser(), GURL(url::kAboutBlankURL));
+  content::SessionStorageNamespace* storage_namespace =
+      GetActiveWebContents()
+          ->GetController()
+          .GetDefaultSessionStorageNamespace();
+
+  std::unique_ptr<TestPrerender> test_prerender =
+      prerender_contents_factory()->ExpectPrerenderContents(
+          FINAL_STATUS_APP_TERMINATING);
+
+  const GURL url =
+      src_server()->GetURL(MakeAbsolute("/prerender/prerender_new_entry.html"));
+  std::unique_ptr<PrerenderHandle> prerender_handle(
+      GetPrerenderManager()->AddPrerenderForOffline(url, storage_namespace,
+                                                    gfx::Size(640, 480)));
+  ASSERT_EQ(prerender_handle->contents(), test_prerender->contents());
+  test_prerender->WaitForLoads(2);
+  ASSERT_EQ(1, GetActiveWebContents()->GetController().GetEntryCount());
+}
+
 // Attempt a swap-in in a new tab. The session storage doesn't match, so it
 // should not swap.
 IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, PrerenderPageNewTab) {

chrome/browser/prerender/prerender_contents.cc

@@ -577,6 +577,13 @@ void PrerenderContents::DidFinishLoad(
 void PrerenderContents::DidNavigateMainFrame(
     const content::LoadCommittedDetails& details,
     const content::FrameNavigateParams& params) {
+  // Prevent ORIGIN_OFFLINE prerenders from being destroyed on location.href
+  // change, since the history is never merged for offline prerenders. Also
+  // avoid adding aliases as they may potentially mark other valid requests to
+  // offline as duplicate.
+  if (origin() == ORIGIN_OFFLINE)
+    return;
+
   // If the prerender made a second navigation entry, abort the prerender. This
   // avoids having to correctly implement a complex history merging case (this
   // interacts with location.replace) and correctly synchronize with the