Add UMA logging of extension creation flags.

extensions/common/extension.h

Index: extensions/common/extension.h
diff --git a/extensions/common/extension.h b/extensions/common/extension.h
index c7b8458193dd8c0e999250bbe55c3a5180b7b7c0..5be02942828fdd3414366b02a46206e97dfac1be 100644
--- a/extensions/common/extension.h
+++ b/extensions/common/extension.h
@@ -117,6 +117,8 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
     virtual ~ManifestData() {}
   };
 
+  // Do not change the order of entries or remove entries in this list
+  // as this is used in UMA_HISTOGRAM_ENUMERATIONs about extensions.
   enum InitFromValueFlags {
     NO_FLAGS = 0,
 
@@ -169,6 +171,7 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
     // be placed in a special OEM folder in the App Launcher. Note: OEM apps are
     // also installed by Default (i.e. WAS_INSTALLED_BY_DEFAULT is also true).
     WAS_INSTALLED_BY_OEM = 1 << 10,
+    LAST_INIT_FROM_VALUE_FLAGS = WAS_INSTALLED_BY_OEM,
   };
 
   static scoped_refptr<Extension> Create(const base::FilePath& path,