Re-enable pre-read experiment as a finch field trial.

chrome/common/chrome_constants.h

 // Copyright (c) 2012 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.
 
 // A handful of resource-like constants related to the Chrome application.
 
 #ifndef CHROME_COMMON_CHROME_CONSTANTS_H_
 #define CHROME_COMMON_CHROME_CONSTANTS_H_
 
 #include "base/files/file_path.h"
@@ skipping 93 matching lines @@
 // Are touch icons enabled? False by default.
 extern const bool kEnableTouchIcon;
 
 // Fraction of the total number of processes to be used for hosting
 // extensions. If we have more extensions than this percentage, we will start
 // combining extensions in existing processes. This allows web pages to have
 // enough render processes and not be starved when a lot of extensions are
 // installed.
 extern const float kMaxShareOfExtensionProcesses;
 
+// This is used by the PreRead experiment.
+extern const char kPreReadEnvironmentVariable[];
+
 #if defined(OS_LINUX)
 // The highest and lowest assigned OOM score adjustment
 // (oom_score_adj) used by the OomPriority Manager.
 extern const int kLowestRendererOomScore;
 extern const int kHighestRendererOomScore;
 #endif
 
 #if defined(OS_WIN)
-// This is used by the PreRead experiment.
-extern const char kPreReadEnvironmentVariable[];
 // Used by Metro Chrome to create the profile under a custom subdirectory.
 extern const wchar_t kMetroChromeUserDataSubDir[];
 // Used by Metro Chrome to initiate navigation and search requests.
 extern const wchar_t kMetroNavigationAndSearchMessage[];
 // Used by Metro Chrome to get information about the current tab.
 extern const wchar_t kMetroGetCurrentTabInfoMessage[];
 // Used by Metro Chrome to store activation state.
 extern const wchar_t kMetroRegistryPath[];
 extern const wchar_t kLaunchModeValue[];
 // Used by the browser as a container in which to track unreported crash dump
 // attempts. The actual values (each representing one crash dump attempt) are
 // stored in a subkey named with the version number of the build. Each value
 // under the subkey represents an additional attempt.
 extern const wchar_t kBrowserCrashDumpAttemptsRegistryPath[];
 #endif
 
 #if defined(OS_CHROMEOS)
 // Chrome OS profile directories have custom prefix.
 // Profile path format: [user_data_dir]/u-[$hash]
 // Ex.: /home/chronos/u-0123456789
 extern const char kProfileDirPrefix[];
 #endif
 
 // Used to identify the application to the system AV function in Windows.
 extern const char kApplicationClientIDStringForAVScanning[];
 
 }  // namespace chrome
 
 #endif  // CHROME_COMMON_CHROME_CONSTANTS_H_