Enable SiteEngagementEvictionPolicy behind --enable-site-eviction-policy flag.

chrome/browser/engagement/site_engagement_eviction_policy.cc

Index: chrome/browser/engagement/site_engagement_eviction_policy.cc
diff --git a/chrome/browser/engagement/site_engagement_eviction_policy.cc b/chrome/browser/engagement/site_engagement_eviction_policy.cc
index a078585ca993f7b16dbc794518331ef5bb16e04e..1ede15c8e525277d6503868ae1f721707fb2c7af 100644
--- a/chrome/browser/engagement/site_engagement_eviction_policy.cc
+++ b/chrome/browser/engagement/site_engagement_eviction_policy.cc
@@ -2,11 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/browser_process.h"
 #include "chrome/browser/engagement/site_engagement_eviction_policy.h"
+
+#include "base/command_line.h"
+#include "base/metrics/field_trial.h"
+#include "base/strings/string_util.h"
+#include "chrome/browser/browser_process.h"
 #include "chrome/browser/engagement/site_engagement_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/common/chrome_switches.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace {
@@ -91,6 +96,19 @@ GURL GetSiteEngagementEvictionOriginOnUIThread(
 
 }  // namespace
 
+// static
+bool SiteEngagementEvictionPolicy::IsEnabled() {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSiteEngagementEvictionPolicy)) {
+    return true;
+  }
+
+  const std::string group_name = base::FieldTrialList::FindFullName(
+      SiteEngagementService::kEngagementParams);
+  return base::StartsWith(group_name, "StorageEvictionEnabled",
+                          base::CompareCase::SENSITIVE);
+}
+
 SiteEngagementEvictionPolicy::SiteEngagementEvictionPolicy(
     content::BrowserContext* browser_context)
     : browser_context_(browser_context) {}