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

components/enhanced_bookmarks/enhanced_bookmark_utils.h

Index: components/enhanced_bookmarks/enhanced_bookmark_utils.h
diff --git a/components/enhanced_bookmarks/enhanced_bookmark_utils.h b/components/enhanced_bookmarks/enhanced_bookmark_utils.h
index c66fa9adf8c07b69bc46c0f791ce27784559797b..81476eb4a4f385dc8b3dde056cd2f9acefa3c3f4 100644
--- a/components/enhanced_bookmarks/enhanced_bookmark_utils.h
+++ b/components/enhanced_bookmarks/enhanced_bookmark_utils.h
@@ -16,6 +16,8 @@ class BookmarkNode;
 
 namespace enhanced_bookmarks {
 
+extern const char kFieldTrialName[];
+
 // Possible locations where a bookmark can be opened from.
 // Please sync with the corresponding histograms.xml.
 //
@@ -31,6 +33,16 @@ enum LaunchLocation {
   COUNT = 6,
 };
 
+// View modes of enhanced bookmarks' main items UI.
+//
+// A Java counterpart will be generated for this enum.
+// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.enhanced_bookmarks
+enum ViewMode {
+  DEFAULT = 0,
+  LIST = 1,
+  GRID = 2,
+};
+
 // Returns the permanent nodes whose url children are considered uncategorized
 // and whose folder children should be shown in the bookmark menu.
 // |model| must be loaded.
@@ -54,6 +66,11 @@ const bookmarks::BookmarkNode* RootLevelFolderForNode(
     const bookmarks::BookmarkNode* node,
     bookmarks::BookmarkModel* model);
 
+// Returns the default view mode for main items UI.
+// The default is controlled by a finch experiment. If finch is not available or
+// has an invalid value, it returns a hard coded default view mode.
+ViewMode GetDefaultViewMode();
+
 }  // namespace enhanced_bookmarks
 
 #endif  // COMPONENTS_ENHANCED_BOOKMARKS_ENHANCED_BOOKMARK_UTILS_H_