IndexedDB: Add histograms for key type

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

Index: third_party/WebKit/Source/modules/indexeddb/IDBKey.h
diff --git a/third_party/WebKit/Source/modules/indexeddb/IDBKey.h b/third_party/WebKit/Source/modules/indexeddb/IDBKey.h
index 4b9ff354ec8b6fc7d97572886c98e97731d8848e..8b45a8f55b2d24aa76d4c97d2d3c8e72018d02ee 100644
--- a/third_party/WebKit/Source/modules/indexeddb/IDBKey.h
+++ b/third_party/WebKit/Source/modules/indexeddb/IDBKey.h
@@ -63,6 +63,7 @@ class MODULES_EXPORT IDBKey : public GarbageCollectedFinalized<IDBKey> {
   DECLARE_TRACE();
 
   // In order of the least to the highest precedent in terms of sort order.
+  // Also used for UMA. Append only.
   enum Type {
     InvalidType = 0,
     ArrayType,
@@ -70,7 +71,7 @@ class MODULES_EXPORT IDBKey : public GarbageCollectedFinalized<IDBKey> {
     StringType,
     DateType,
     NumberType,
-    MinType
+    TypeEnumMax = NumberType
   };
 
   Type getType() const { return m_type; }