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

chrome/browser/chrome_browser_field_trials_desktop.h

+// 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.
+
+#ifndef CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_DESKTOP_H_
+#define CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_DESKTOP_H_
+
+#include "base/basictypes.h"
+#include "base/time.h"
+
+class CommandLine;
+class PrefService;
+
+namespace chrome {
+
+// Sets up common desktop-only field trials.
+// Add an invocation of your field trial init function to this method, or to
+// SetupFieldTrials in chrome_browser_field_trials.cc if it is for all
+// platforms.
+// |local_state| is needed by some other methods called from within this one.
+void SetupDesktopFieldTrials(const CommandLine& parsed_command_line,
+                             const base::Time& install_time,
+                             PrefService* local_state);
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_DESKTOP_H_