Report the wasted network bytes when resource prefetches hit max limit

components/precache/core/precache_fetcher.cc

 // Copyright 2013 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 "components/precache/core/precache_fetcher.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 #include <utility>
@@ skipping 225 matching lines @@
   // If going over the per-resource download cap.
   if (fetch_stage_ == FetchStage::NETWORK &&
       // |current| is guaranteed to be non-negative, so this cast is safe.
       static_cast<size_t>(std::max(current, total)) > max_bytes_) {
     VLOG(1) << "Cancelling " << url_ << ": (" << current << "/" << total
             << ") is over " << max_bytes_;
 
     // Cancel the download.
     network_url_fetcher_.reset();
 
+    response_bytes_ = network_response_bytes_ = current;
+
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Precache.Fetch.ResponseBytes.NetworkWasted",
+                                network_response_bytes_, 1, kMaxResponseBytes,
+                                100);
+
     // Call the completion callback, to attempt the next download, or to trigger
     // cleanup in precache_delegate_->OnDone().
-    response_bytes_ = network_response_bytes_ = current;
-
     callback_.Run(*this);
   }
 }
 
 void PrecacheFetcher::Fetcher::OnURLFetchComplete(
     const net::URLFetcher* source) {
   CHECK(source);
   if (fetch_stage_ == FetchStage::CACHE &&
       (source->GetStatus().error() == net::ERR_CACHE_MISS ||
        (source->GetResponseHeaders() &&
@@ skipping 311 matching lines @@
 
 void PrecacheFetcher::UpdateStats(int64_t response_bytes,
                                   int64_t network_response_bytes) {
   unfinished_work_->set_total_bytes(
       unfinished_work_->total_bytes() + response_bytes);
   unfinished_work_->set_network_bytes(
       unfinished_work_->network_bytes() + network_response_bytes);
 }
 
 }  // namespace precache