FieldTrial implementation for webrtc.

BUG=crbug/367114
R=asvitkine@chromium.org, mflodman@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/14399004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6089 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/system_wrappers/interface/field_trial.h

@@ -0,0 +1,67 @@
+//
+// Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+//
+
+#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_FIELD_TRIAL_H_
+#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_FIELD_TRIAL_H_
+
+#include <string>
+
+#include "webrtc/common_types.h"
+
+// Field trials allow a client of webrtc (such as Chrome) to turn on feature
+// code in binraries out in the field and gather information with that.
+// WebRTC field trials are designed to be wired up directly to chrome field
+// trials and speed up the time developers need to get features out there by
+// spending less time wiring up APIs to control whether the feature is on/off.
+// Note, that not every feature is candidate to be controlled by them as it may
+// require proper negotiation between involved parties (e.g. SDP negotiation).
+//
+// E.g.: To experiment with a new method that could lead to a different
+// trade-off between CPU/bandwidth:
+//
+// 1 - Develop the feature with default behaviour off:
+//
+//   if (FieldTrial::FindFullName("WebRTCExperimenMethod2") == "Enabled")
+//     method2();
+//   else
+//     method1();
+//
+// 2 - Once the changes are rolled to chrome, the new code path can be executed
+// by running chrome with --force-fieldtrials=WebRTCExperimentMethod2/Enabled/
+// or controled by finch studies.
+//
+// 3 - Evaluate the new feature and clean the code paths.
+//
+// TODO(andresp): find out how to get bots and unit tests to run with field
+// trials enabled.
+
+namespace webrtc {
+namespace field_trial {
+
+typedef std::string (*FindFullNameMethod)(const std::string&);
+
+// Returns the group name chosen for the named trial, or the empty string
+// if the trial does not exists.
+//
+// Note: To keep things tidy append all the trial names with WebRTC.
+std::string FindFullName(const std::string& name);
+
+// WebRTC clients MUST call this method to setup field trials.
+// Failing to do so will crash the first time code tries to access a field
+// trial.
+//
+// This method must be called before any WebRTC methods. Functions
+// provided should be thread-safe.
+WEBRTC_DLLEXPORT void Init(FindFullNameMethod find);
+
+}  // namespace field_trial
+}  // namespace webrtc
+
+#endif  // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_FIELD_TRIAL_H_

webrtc/system_wrappers/source/field_trial.cc

@@ -0,0 +1,30 @@
+// Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+//
+
+#include "webrtc/system_wrappers/interface/field_trial.h"
+
+#include <cassert>
+
+namespace webrtc {
+namespace field_trial {
+namespace {
+FindFullNameMethod find_full_name_method_ = NULL;
+}  // namespace
+
+void Init(FindFullNameMethod method) {
+  assert(find_full_name_method_ == NULL);
+  find_full_name_method_ = method;
+}
+
+std::string FindFullName(const std::string& name) {
+  assert(find_full_name_method_ != NULL);
+  return find_full_name_method_(name);
+}
+}  // namespace field_trial
+}  // namespace webrtc

webrtc/system_wrappers/source/system_wrappers.gyp

@@ -35,6 +35,7 @@
         '../interface/data_log_impl.h',
         '../interface/event_tracer.h',
         '../interface/event_wrapper.h',
+        '../interface/field_trial.h',
         '../interface/file_wrapper.h',
         '../interface/fix_interlocked_exchange_pointer_win.h',
         '../interface/logcat_trace_context.h',
@@ -85,6 +86,7 @@
         'event_tracer.cc',
         'event_win.cc',
         'event_win.h',
+	'field_trial.cc',
         'file_impl.cc',
         'file_impl.h',
         'logcat_trace_context.cc',