Added an experiment for an LRU snapshot cache.

ios/chrome/browser/chrome_switches.cc

 // Copyright 2015 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 "ios/chrome/browser/chrome_switches.h"
 
 namespace switches {
 
 // -----------------------------------------------------------------------------
 // When commenting your switch, please use the same voice as surrounding
@@ skipping 13 matching lines @@
 // Disables support for keyboard commands.
 const char kDisableKeyboardCommands[] = "disable-keyboard-commands";
 
 // Enables the recording of metrics reports but disables reporting. In contrast
 // to kDisableMetrics, this executes all the code that a normal client would
 // use for reporting, except the report is dropped rather than sent to the
 // server. This is useful for finding issues in the metrics code during UI and
 // performance tests.
 const char kIOSMetricsRecordingOnly[] = "metrics-recording-only";
 
+// Disable the snapshots lru cache.
+const char kDisableLRUSnapshotCache[] = "disable-lru-snapshot-cache";
+
+// Enables the snapshot lru cache.
+const char kEnableLRUSnapshotCache[] = "enable-lru-snapshot-cache";
+
 }  // namespace switches