Safely set Server Lite Page Status during redirects and failures

This is causing infrequent crashes in the Canary/Dev experiment. See
bug. This is due to the WebLite client redirect issue that caused Issue
913639, but could in theory be caused by any navigation to the litepages
domain that is not started by our NavThrottle.

Bug: 919049
Change-Id: Ic309d9d4f63c7b3d3bc8de742ef58213042eedbe
Reviewed-on: https://chromium-review.googlesource.com/c/1396322Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620020}

chrome/browser/previews/previews_lite_page_navigation_throttle.cc

@@ -541,7 +541,7 @@ PreviewsLitePageNavigationThrottle::WillRedirectRequest() {
     // it is pointing towards the original page, it is considered a bypass.
     // Otherwise it is just a forwarded bypass.
     if (GURL(original_url) == navigation_handle()->GetURL()) {
-      GetServerLitePageInfo()->status = previews::ServerLitePageStatus::kBypass;
+      SetServerLitePageInfoStatus(previews::ServerLitePageStatus::kBypass);
       manager_->AddSingleBypass(navigation_handle()->GetURL().spec());
       UMA_HISTOGRAM_MEDIUM_TIMES(
           "Previews.ServerLitePage.HttpOnlyFallbackPenalty",
@@ -574,7 +574,7 @@ PreviewsLitePageNavigationThrottle::WillRedirectRequest() {
     // Otherwise fall out of this if and potentially trigger again.
     UMA_HISTOGRAM_ENUMERATION("Previews.ServerLitePage.ServerResponse",
                               ServerResponse::kRedirect);
-    GetServerLitePageInfo()->status = previews::ServerLitePageStatus::kRedirect;
+    SetServerLitePageInfoStatus(previews::ServerLitePageStatus::kRedirect);
   }
 
   return MaybeNavigateToPreview();
@@ -590,7 +590,7 @@ PreviewsLitePageNavigationThrottle::WillFailRequest() {
 
   UMA_HISTOGRAM_ENUMERATION("Previews.ServerLitePage.ServerResponse",
                             ServerResponse::kFailed);
-  GetServerLitePageInfo()->status = previews::ServerLitePageStatus::kFailure;
+  SetServerLitePageInfoStatus(previews::ServerLitePageStatus::kFailure);
 
   // The Preview was triggered but there was some irrecoverable issue (like
   // there is no network connection). Load the original page and let it go
@@ -598,7 +598,8 @@ PreviewsLitePageNavigationThrottle::WillFailRequest() {
   LoadAndBypass(
       navigation_handle()->GetWebContents(), manager_,
       MakeOpenURLParams(navigation_handle(), GURL(original_url), std::string()),
-      GetServerLitePageInfo()->Clone(), true);
+      GetServerLitePageInfo() ? GetServerLitePageInfo()->Clone() : nullptr,
+      true);
   return content::NavigationThrottle::CANCEL;
 }
 
@@ -690,6 +691,15 @@ PreviewsLitePageNavigationThrottle::GetServerLitePageInfo() const {
   return previews_data->server_lite_page_info();
 }
 
+void PreviewsLitePageNavigationThrottle::SetServerLitePageInfoStatus(
+    previews::ServerLitePageStatus status) {
+  previews::PreviewsUserData::ServerLitePageInfo* info =
+      GetServerLitePageInfo();
+  if (!info)
+    return;
+  info->status = status;
+}
+
 previews::PreviewsUserData::ServerLitePageInfo*
 PreviewsLitePageNavigationThrottle::GetOrCreateServerLitePageInfo() const {
   PreviewsUITabHelper* ui_tab_helper = PreviewsUITabHelper::FromWebContents(

chrome/browser/previews/previews_lite_page_navigation_throttle.h

@@ -142,6 +142,10 @@ class PreviewsLitePageNavigationThrottle : public content::NavigationThrottle {
   // navigation, if there is one. If not, returns nullptr.
   previews::PreviewsUserData::ServerLitePageInfo* GetServerLitePageInfo() const;
 
+  // Safely sets the status of the ServerLitePageInfo struct from an existing
+  // attempted lite page navigation, if there is one. If not, does nothing.
+  void SetServerLitePageInfoStatus(previews::ServerLitePageStatus status);
+
   // Gets the ServerLitePageInfo struct from an existing attempted lite page
   // navigation, if there is one. If not, returns a new ServerLitePageInfo
   // initialized with metadata from navigation_handle() and |this| that is owned