[Android] Add enhanced bookmarks grid/list view experiment.

components/enhanced_bookmarks/enhanced_bookmark_utils.cc

 // 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.
 
 #include "components/enhanced_bookmarks/enhanced_bookmark_utils.h"
 
 #include "components/bookmarks/browser/bookmark_model.h"
+#include "components/variations/variations_associated_data.h"
 
 using bookmarks::BookmarkModel;
 using bookmarks::BookmarkNode;
 
 namespace enhanced_bookmarks {
 
+const char kFieldTrialName[] = "EnhancedBookmarks";
+
 std::vector<const BookmarkNode*> PrimaryPermanentNodes(BookmarkModel* model) {
   DCHECK(model->loaded());
   std::vector<const BookmarkNode*> nodes;
   nodes.push_back(model->mobile_node());
   nodes.push_back(model->bookmark_bar_node());
   nodes.push_back(model->other_node());
   return nodes;
 }
 
 std::vector<const BookmarkNode*> RootLevelFolders(BookmarkModel* model) {
@@ skipping 32 matching lines @@
   const std::vector<const BookmarkNode*> root_folders(RootLevelFolders(model));
   const BookmarkNode* top = node;
   while (top &&
          std::find(root_folders.begin(), root_folders.end(), top) ==
              root_folders.end()) {
     top = top->parent();
   }
   return top;
 }
 
+ViewMode GetDefaultViewMode() {
+  std::string default_view_mode = variations::GetVariationParamValue(
+      enhanced_bookmarks::kFieldTrialName, "DefaultViewMode");
+
+  if (default_view_mode == "List") return ViewMode::LIST;
+
+  // Below line was ommitted because the default is ViewMode::GRID anyways.
+  // if (default_view_mode == "Grid") return ViewMode::GRID;

[Theresa, 2015/05/28 20:13:08]

If we change the default to list (or something else) later, this line will be
needed again? The default controlled by finch, yes?

[Kibeom Kim (inactive), 2015/05/29 00:11:04]

Sorry. The comment and the structure was confusing.. clarified it. Done.

+
+  return ViewMode::GRID;
+}
+
 }  // namespace enhanced_bookmarks