Select precache resources based on field trial experiment group

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 105 matching lines @@
     return false;
   }
   if (!message->ParseFromString(response_string)) {
     DLOG(WARNING) << "Unable to parse proto served from "
                   << source.GetOriginalURL().spec();
     return false;
   }
   return true;
 }
 
+// Returns the resource selection bitset from the |manifest| for the given
+// |experiment_id|. By default all resource will be selected if the experiment
+// group is not found.
+uint64_t GetResourceBitset(const PrecacheManifest& manifest,
+                           uint32_t experiment_id) {
+  if (manifest.has_experiments()) {
+    const auto& resource_bitset_map =
+        manifest.experiments().resources_by_experiment_group();
+    const auto& resource_bitset_it = resource_bitset_map.find(experiment_id);
+    if (resource_bitset_it != resource_bitset_map.end())
+      return resource_bitset_it->second.bitset();
+  }
+  return ~0ULL;
+}
+
 // URLFetcherResponseWriter that ignores the response body, in order to avoid
 // the unnecessary memory usage. Use it rather than the default if you don't
 // care about parsing the response body. We use it below as a means to populate
 // the cache with requested resource URLs.
 class URLFetcherNullWriter : public net::URLFetcherResponseWriter {
  public:
   int Initialize(const net::CompletionCallback& callback) override {
     return net::OK;
   }
 
@@ skipping 163 matching lines @@
                               unfinished_work.network_bytes(),
                               1, kMaxResponseBytes,
                               100);
 }
 
 PrecacheFetcher::PrecacheFetcher(
     net::URLRequestContextGetter* request_context,
     const GURL& config_url,
     const std::string& manifest_url_prefix,
     std::unique_ptr<PrecacheUnfinishedWork> unfinished_work,
+    uint32_t experiment_id,
     PrecacheFetcher::PrecacheDelegate* precache_delegate)
     : request_context_(request_context),
       config_url_(config_url),
       manifest_url_prefix_(manifest_url_prefix),
       precache_delegate_(precache_delegate),
-      pool_(kMaxParallelFetches) {
+      pool_(kMaxParallelFetches),
+      experiment_id_(experiment_id) {
   DCHECK(request_context_.get());  // Request context must be non-NULL.
   DCHECK(precache_delegate_);  // Precache delegate must be non-NULL.
 
   DCHECK_NE(GURL(), GetDefaultConfigURL())
       << "Could not determine the precache config settings URL.";
   DCHECK_NE(std::string(), GetDefaultManifestURLPrefix())
       << "Could not determine the default precache manifest URL prefix.";
   DCHECK(unfinished_work);
 
   // Copy manifests and resources to member variables as a convenience.
@@ skipping 189 matching lines @@
   UpdateStats(source.response_bytes(), source.network_response_bytes());
   if (source.network_url_fetcher() == nullptr) {
     pool_.DeleteAll();  // Cancel any other ongoing request.
   } else {
     PrecacheManifest manifest;
 
     if (ParseProtoFromFetchResponse(*source.network_url_fetcher(), &manifest)) {
       const int32_t len =
           std::min(manifest.resource_size(),
                    unfinished_work_->config_settings().top_resources_count());
+      const uint64_t resource_bitset =
+          GetResourceBitset(manifest, experiment_id_);
       for (int i = 0; i < len; ++i) {
-        if (manifest.resource(i).has_url())
+        if (((0x1ULL << i) & resource_bitset) && manifest.resource(i).has_url())
           resource_urls_to_fetch_.push_back(GURL(manifest.resource(i).url()));
       }
     }
   }
 
   pool_.Delete(source);
   StartNextFetch();
 }
 
 void PrecacheFetcher::OnResourceFetchComplete(const Fetcher& source) {
   UpdateStats(source.response_bytes(), source.network_response_bytes());
   pool_.Delete(source);
   // The resource has already been put in the cache during the fetch process, so
   // nothing more needs to be done for the resource.
   StartNextFetch();
 }
 
 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