Added an experiment for an LRU snapshot cache.

ios/chrome/browser/experimental_flags.mm

 // 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.
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // definitions required for experimental flags.
 
 #include "ios/chrome/browser/experimental_flags.h"
 
 #import <Foundation/Foundation.h>
@@ skipping 36 matching lines @@
 
 void SetWKWebViewTrialEligibility(bool eligible) {
   // It's critical that the enabled state be consistently reported throughout
   // the life of the app, so ensure that this has not already been set.
   DCHECK(g_wkwebview_trial_eligibility == WKWebViewEligibility::UNSET);
 
   g_wkwebview_trial_eligibility = eligible ? WKWebViewEligibility::ELIGIBLE
                                            : WKWebViewEligibility::INELIGIBLE;
 }
 
+bool IsLRUSnapshotCacheEnabled() {
+  // Check if the experimental flag is forced on or off.
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kEnableLRUSnapshotCache)) {
+    return true;
+  } else if (command_line->HasSwitch(switches::kDisableLRUSnapshotCache)) {
+    return false;
+  }
+
+  // Check if the finch experiment is turned on.
+  std::string group_name =
+      base::FieldTrialList::FindFullName("IOSLRUSnapshotCache");
+  return base::StartsWith(group_name, "Enabled",
+                          base::CompareCase::INSENSITIVE_ASCII);
+}
+
 bool IsWKWebViewEnabled() {
   // If g_wkwebview_trial_eligibility hasn't been set, default it to
   // ineligibile. This ensures future calls to try to set it will DCHECK.
   if (g_wkwebview_trial_eligibility == WKWebViewEligibility::UNSET) {
     g_wkwebview_trial_eligibility = WKWebViewEligibility::INELIGIBLE;
   }
 
   // If WKWebView isn't supported, don't activate the experiment at all. This
   // avoids someone being slotted into the WKWebView bucket (and thus reporting
   // as WKWebView), but actually running UIWebView.
@@ skipping 37 matching lines @@
 
 bool IsViewCopyPasswordsEnabled() {
   NSString* viewCopyPasswordFlag = [[NSUserDefaults standardUserDefaults]
       objectForKey:kEnableViewCopyPasswords];
   if ([viewCopyPasswordFlag isEqualToString:@"Enabled"])
     return true;
   return false;
 }
 
 }  // namespace experimental_flags