Check the return value when canceling prerenders.

chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc

Index: chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
diff --git a/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc b/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
index 063460e8c548fe80a617907b4fdef2a54ba53df6..f18cf48dc0227c71ead1c0221eda8b8abef14122 100644
--- a/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
+++ b/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
@@ -228,15 +228,15 @@ bool ChromeResourceDispatcherHostDelegate::ShouldBeginRequest(
   // Abort any prerenders that spawn requests that use invalid HTTP methods
   // or invalid schemes.
   if (prerender_tracker_->IsPrerenderingOnIOThread(child_id, route_id)) {
-    if (!prerender::PrerenderManager::IsValidHttpMethod(method)) {
-      prerender_tracker_->TryCancelOnIOThread(
-          child_id, route_id, prerender::FINAL_STATUS_INVALID_HTTP_METHOD);
+    if (!prerender::PrerenderManager::IsValidHttpMethod(method) &&
+        prerender_tracker_->TryCancelOnIOThread(
+            child_id, route_id, prerender::FINAL_STATUS_INVALID_HTTP_METHOD)) {
       return false;
     }
-    if (!prerender::PrerenderManager::DoesSubresourceURLHaveValidScheme(url)) {
+    if (!prerender::PrerenderManager::DoesSubresourceURLHaveValidScheme(url) &&
+        prerender_tracker_->TryCancelOnIOThread(
+            child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME)) {
       ReportUnsupportedPrerenderScheme(url);
-      prerender_tracker_->TryCancelOnIOThread(
-          child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME);
       return false;
     }
   }
@@ -425,11 +425,11 @@ bool ChromeResourceDispatcherHostDelegate::HandleExternalProtocol(
   return false;
 #else
 
-  if (prerender_tracker_->IsPrerenderingOnIOThread(child_id, route_id)) {
+  if (prerender_tracker_->IsPrerenderingOnIOThread(child_id, route_id) &&
+      prerender_tracker_->TryCancel(
+          child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME)) {
     ReportPrerenderSchemeCancelReason(
         PRERENDER_SCHEME_CANCEL_REASON_EXTERNAL_PROTOCOL);
-    prerender_tracker_->TryCancel(
-        child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME);
     return false;
   }
 
@@ -651,10 +651,10 @@ void ChromeResourceDispatcherHostDelegate::OnRequestRedirected(
   if (!prerender::PrerenderManager::DoesURLHaveValidScheme(redirect_url) &&
       ResourceRequestInfo::ForRequest(request)->GetAssociatedRenderView(
           &child_id, &route_id) &&
-      prerender_tracker_->IsPrerenderingOnIOThread(child_id, route_id)) {
+      prerender_tracker_->IsPrerenderingOnIOThread(child_id, route_id) &&
+      prerender_tracker_->TryCancel(
+          child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME)) {
     ReportUnsupportedPrerenderScheme(redirect_url);
-    prerender_tracker_->TryCancel(
-        child_id, route_id, prerender::FINAL_STATUS_UNSUPPORTED_SCHEME);
     request->Cancel();
   }
 }