[Android] Add a field trial to disable enhanced bookmark image saving.

chrome/browser/bookmarks/enhanced_bookmarks_features.cc

 // Copyright 2013 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 "chrome/browser/bookmarks/enhanced_bookmarks_features.h"
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
@@ skipping 156 matching lines @@
 bool IsEnhancedBookmarksExperimentEnabled() {
   CommandLine* command_line = CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kManualEnhancedBookmarks) ||
       command_line->HasSwitch(switches::kManualEnhancedBookmarksOptout)) {
     return true;
   }
 
   return IsEnhancedBookmarksExperimentEnabledFromFinch();
 }
 
+#if defined(OS_ANDROID)
+bool IsEnhancedBookmarkImageFetchingEnabled() {
+  if (IsEnhancedBookmarksExperimentEnabled())
+    return true;
+
+  // Salient images are collected from visited bookmarked pages even if the
+  // enhanced bookmark feature is turned off. This is to have some images
+  // available so that in the future, when the feature is turned on, the user
+  // experience is not a big list of flat colors. However as a precautionary
+  // measure it is possible to disable this collection of images from finch.
+  std::string disable_fetching = chrome_variations::GetVariationParamValue(
+      kFieldTrialName, "DisableImagesFetching");
+  return disable_fetching.empty();
+}
+#endif
+
 bool IsEnableDomDistillerSet() {
   if (CommandLine::ForCurrentProcess()->
       HasSwitch(switches::kEnableDomDistiller)) {
     return true;
   }
   if (chrome_variations::GetVariationParamValue(
           kFieldTrialName, "enable-dom-distiller") == "1")
     return true;
 
   return false;
 }
 
 bool IsEnableSyncArticlesSet() {
   if (CommandLine::ForCurrentProcess()->
       HasSwitch(switches::kEnableSyncArticles)) {
     return true;
   }
   if (chrome_variations::GetVariationParamValue(
           kFieldTrialName, "enable-sync-articles") == "1")
     return true;
 
   return false;
 }