precache: Allow experiment bitsets of any size.

components/precache/core/proto/precache.proto

 // 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.
 
 syntax = "proto2";
 
 package precache;
 
 // Chrome requires this.
 option optimize_for = LITE_RUNTIME;
@@ skipping 27 matching lines @@
   // Identifier for the manifest sent by the server.
   optional PrecacheManifestId id = 3;
 };
 
 message PrecacheExperiments {
   // A mapping between experiment groups and the resources that should be
   // considered for the experiment.
   map<fixed32, PrecacheResourceSelection> resources_by_experiment_group = 1;
 };
 
+// Determines which of the resources in the manifest should be selected.
 message PrecacheResourceSelection {
-  // Select the resources as a std::bitset over the resources listed in the
-  // manifest.
+  // A bitset over the resources listed in the manifest. Bits correspond to
+  // resource position in LSB-to-MSB order, as in:
   //
-  // The bitset should be loaded as:
-  //   std::bitset selection(resource_selection.bitset());
-  // Then manifest.resource(i) is selected for the experiment iff
-  // selection.test(i).
+  //   if ((0x1ULL << i) && DEPRECATED_bitset) IncludeResource(i);
   //
-  // A missing bitset means that the experiment applies to all the resources.
-  optional fixed64 bitset = 1 [default = 0xFFFFFFFFFFFFFFFF];
+  // Deprecated because it only supports up to 64 resources.
+  optional fixed64 DEPRECATED_bitset = 1
+      [default = 0xFFFFFFFFFFFFFFFF, deprecated = true];
+
+  // A bitset over the resources listed in the manifest. Bits correspond to
+  // resource position. Bytes are ordered little-endian, and bits within each
+  // byte are ordered LSB-to-MSB. The resulting bitstream is of mixed order,
+  // but easy to test:
+  //
+  //   if ((1 << (i % 8)) & bitset[i / 8]) IncludeResource(i);
+  //
+  // Takes precedence over DEPRECATED_bitset, if both are present.
+  optional bytes bitset = 2;
+
+  // A PrecacheResourceSelection without DEPRECATED_bitset or bitset means that
+  // all resources should be selected.
 };
 
 message PrecacheConfigurationSettings {
   // The maximum rank of the user's most visited hosts to consider precaching
   // resources for, starting from 1. For example, a value of 10 means that only
   // hosts that are in the user's top 10 most visited hosts will be considered
   // as starting URLs for resource precaching. This is specified by the server
   // for testing purposes, so that it's easy to adjust how aggressively
   // resources are precached.
   // Values that are zero or lower indicate that none of the user's top sites
@@ skipping 48 matching lines @@
     // days, given that weight_ratio is a probability that a visit to the host
     // will request a resource, and host_visits is an estimate of the number of
     // visits to the host in the next 30 days.
     FUNCTION_NAIVE = 0;
     // Models the probability of at least one request, given the same.
     FUNCTION_GEOMETRIC = 1;
   };
   optional ResourceWeightFunction resource_weight_function = 11
       [default = FUNCTION_NAIVE];
 };