PlzNavigate: Add metrics to understand bf navigations PLT regression

content/browser/loader/resource_loader.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/loader/resource_loader.h"
 
 #include <utility>
 
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
@@ skipping 628 matching lines @@
   }
 }
 
 void ResourceLoader::CompleteResponseStarted() {
   ResourceRequestInfoImpl* info = GetRequestInfo();
   scoped_refptr<ResourceResponse> response = new ResourceResponse();
   PopulateResourceResponse(info, request_.get(), response.get());
 
   delegate_->DidReceiveResponse(this, response.get());
 
+  // For back-forward navigations, record metrics.
+  // TODO(clamy): Remove once we understand the root cause behind the regression
+  // of PLT for b/f navigations in PlzNavigate.
+  if ((info->GetPageTransition() & ui::PAGE_TRANSITION_FORWARD_BACK) &&
+      IsResourceTypeFrame(info->GetResourceType()) &&
+      !request_->url().SchemeIsBlob()) {
+    UMA_HISTOGRAM_BOOLEAN("Navigation.BackForward.WasCached",
+                          request_->was_cached());
+  }
+
   read_deferral_start_time_ = base::TimeTicks::Now();
   // Using a ScopedDeferral here would result in calling ReadMore(true) on sync
   // success. Calling PrepareToReadMore(false) here instead allows small
   // responses to be handled completely synchronously, if no ResourceHandler
   // defers handling of the response.
   deferred_stage_ = DEFERRED_SYNC;
   handler_->OnResponseStarted(response.get(),
                               base::MakeUnique<Controller>(this));
   if (is_deferred()) {
     deferred_stage_ = DEFERRED_READ;
@@ skipping 148 matching lines @@
       UMA_HISTOGRAM_ENUMERATION("Net.Prefetch.Pattern", prefetch_status,
                                 STATUS_MAX);
     }
   } else if (request_->response_info().unused_since_prefetch) {
     TimeDelta total_time = base::TimeTicks::Now() - request_->creation_time();
     UMA_HISTOGRAM_TIMES("Net.Prefetch.TimeSpentOnPrefetchHit", total_time);
   }
 }
 
 }  // namespace content