Adds UMA for PrerenderingOffliner request processing result status.

chrome/browser/android/offline_pages/prerendering_loader.cc

Index: chrome/browser/android/offline_pages/prerendering_loader.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_loader.cc b/chrome/browser/android/offline_pages/prerendering_loader.cc
index b82a149ab9ddb0be4d9b23bb4c051f37614d5029..6f454028d33ae1ed2e3157747b55aca825368e9b 100644
--- a/chrome/browser/android/offline_pages/prerendering_loader.cc
+++ b/chrome/browser/android/offline_pages/prerendering_loader.cc
@@ -164,8 +164,8 @@ void PrerenderingLoader::HandleLoadingStopped() {
   // Request status depends on whether we are still loading (failed) or
   // did load and then loading was stopped (cancel - from prerender stack).
   Offliner::RequestStatus request_status =
-      IsLoaded() ? Offliner::RequestStatus::CANCELED
-                 : Offliner::RequestStatus::FAILED;
+      IsLoaded() ? Offliner::RequestStatus::PRERENDERING_CANCELED
+                 : Offliner::RequestStatus::PRERENDERING_FAILED;
   // TODO(dougarnett): For failure, determine from final status if retry-able
   // and report different failure statuses if retry-able or not.
   snapshot_controller_.reset(nullptr);
@@ -181,11 +181,6 @@ void PrerenderingLoader::CancelPrerender() {
   }
   snapshot_controller_.reset(nullptr);
   session_contents_.reset(nullptr);
-  if (!IsLoaded() && !IsIdle()) {
-    base::ThreadTaskRunnerHandle::Get()->PostTask(
-        FROM_HERE,
-        base::Bind(callback_, Offliner::RequestStatus::CANCELED, nullptr));
-  }
   state_ = State::IDLE;
 }