IndexedDB: Add histograms for key type

third_party/WebKit/Source/modules/indexeddb/IDBKey.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 45 matching lines @@
   static IDBKey* createDate(double date) { return new IDBKey(DateType, date); }
 
   static IDBKey* createArray(const KeyArray& array) {
     return new IDBKey(array);
   }
 
   ~IDBKey();
   DECLARE_TRACE();
 
   // In order of the least to the highest precedent in terms of sort order.
+  // These values are written to logs. New enum values can be added, but
+  // existing enums must never be renumbered or deleted and reused.
   enum Type {
     InvalidType = 0,
-    ArrayType,
-    BinaryType,
-    StringType,
-    DateType,
-    NumberType,
-    MinType
+    ArrayType = 1,
+    BinaryType = 2,
+    StringType = 3,
+    DateType = 4,
+    NumberType = 5,
+    TypeEnumMax = 6,

[Mark P, 2017/02/07 22:59:46]

nit: leave max unassigned; it will default to 6.  Then it becomes easier that
it's okay to change the max value.

   };
 
   Type getType() const { return m_type; }
   bool isValid() const;
 
   const KeyArray& array() const {
     ASSERT(m_type == ArrayType);
     return m_array;
   }
 
@@ skipping 36 matching lines @@
   const Type m_type;
   const KeyArray m_array;
   RefPtr<SharedBuffer> m_binary;
   const String m_string;
   const double m_number = 0;
 };
 
 }  // namespace blink
 
 #endif  // IDBKey_h