Split the field trial setup code into desktop and mobile files.

chrome/browser/chrome_browser_field_trials_mobile.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 "chrome/browser/chrome_browser_field_trials_mobile.h"
+
+#include <string>
+
+#include "base/command_line.h"
+#include "base/metrics/field_trial.h"
+#include "base/prefs/pref_service.h"
+#include "chrome/common/chrome_version_info.h"
+
+namespace chrome {
+
+namespace {
+
+// Governs the rollout of the compression proxy for Chrome on mobile platforms.
+// Always enabled in DEV and BETA versions.

[Nico, 2014/04/22 22:08:33]

I saw this today. What's the motivation for this? It seems that beta and dev
should test what we ship to stable, at least by some percentage. As is, beta and
dev only test the compression proxy, and then we launch to stable and the
non-compression-codepath has had almost no testing in the field.

[marq (ping after 24h), 2014/04/24 00:45:32]

Nico,

This trial just gated exposure of the settings control for users to enable the
proxy. There wasn't a "non-compression" codepath that didn't get exercised (even
with the proxy on, https and incognito tabs weren't proxied).

In any case, this has been a 100% stable feature for several milestones, and
this code will probabaly be removed in the near future.

+// Stable percentage will be controlled from server.
+void DataCompressionProxyFieldTrial() {
+  const char kDataCompressionProxyFieldTrialName[] =
+      "DataCompressionProxyRollout";
+  const base::FieldTrial::Probability kDataCompressionProxyDivisor = 1000;
+
+  // 10/1000 = 1% for starters.
+  const base::FieldTrial::Probability kDataCompressionProxyStable = 10;
+  const char kEnabled[] = "Enabled";
+  const char kDisabled[] = "Disabled";
+
+  // Find out if this is a stable channel.
+  const bool kIsStableChannel =
+      chrome::VersionInfo::GetChannel() == chrome::VersionInfo::CHANNEL_STABLE;
+
+  // Experiment enabled until Jan 1, 2015. By default, disabled.
+  scoped_refptr<base::FieldTrial> trial(
+      base::FieldTrialList::FactoryGetFieldTrial(
+          kDataCompressionProxyFieldTrialName, kDataCompressionProxyDivisor,
+          kDisabled, 2015, 1, 1, NULL));
+
+  // We want our trial results to be persistent.
+  trial->UseOneTimeRandomization();
+  // Non-stable channels will run with probability 1.
+  const int kEnabledGroup = trial->AppendGroup(
+      kEnabled,
+      kIsStableChannel ?
+          kDataCompressionProxyStable : kDataCompressionProxyDivisor);
+
+  const int v = trial->group();
+  VLOG(1) << "DataCompression proxy enabled group id: " << kEnabledGroup
+          << ". Selected group id: " << v;
+}
+
+}  // namespace
+
+void SetupMobileFieldTrials(const CommandLine& parsed_command_line,
+                            const base::Time& install_time,
+                            PrefService* local_state) {
+  DataCompressionProxyFieldTrial();
+}
+
+}  // namespace chrome