Added an experiment for an LRU snapshot cache.

ios/chrome/browser/experimental_flags.h

 // Copyright 2014 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 IOS_CHROME_BROWSER_EXPERIMENTAL_FLAGS_H_
 #define IOS_CHROME_BROWSER_EXPERIMENTAL_FLAGS_H_
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // declarations required for experimental flags.
 
 namespace experimental_flags {
 
 // Whether background crash report upload should generate a local notification.
 bool IsAlertOnBackgroundUploadEnabled();
 
 // Whether the new bookmark collection experience is enabled.
 bool IsBookmarkCollectionEnabled();
 
 // Sets whether or not the field trial for WKWebView should be enabled. This
 // must be called at most once, and before IsWKWebViewEnabled. If this is never
 // called, IsWKWebViewEnabled will assume ineligibility.
 // Note that an explicit command line flag will ignore this setting; it controls
 // only whether the trial state will be checked in the default state.
 void SetWKWebViewTrialEligibility(bool eligible);
 
+// Whether the lru snapshot cache experiment is enabled.
+bool IsLRUSnapshotCacheEnabled();
+
 // Whether the app uses WKWebView instead of UIWebView.
 // The returned value will not change within a given session.
 bool IsWKWebViewEnabled();
 
 // Whether keyboard commands are supported.
 bool AreKeyboardCommandsEnabled();
 
 // Whether viewing and copying passwords is enabled.
 bool IsViewCopyPasswordsEnabled();
 
 }  // namespace experimental_flags
 
 #endif  // IOS_CHROME_BROWSER_EXPERIMENTAL_FLAGS_H_