Use a two-part data format version in IndexedDB metadata.

third_party/WebKit/public/web/WebSerializedScriptValueVersion.h

Index: third_party/WebKit/public/web/WebSerializedScriptValueVersion.h
diff --git a/third_party/WebKit/public/web/WebSerializedScriptValueVersion.h b/third_party/WebKit/public/web/WebSerializedScriptValueVersion.h
index a808ae23fedda2fd79b7392ff8e258f50049c2c9..9a4b3d26c06c4068b1dfb2966dff9eb2d08f9293 100644
--- a/third_party/WebKit/public/web/WebSerializedScriptValueVersion.h
+++ b/third_party/WebKit/public/web/WebSerializedScriptValueVersion.h
@@ -31,14 +31,29 @@
 #ifndef WebSerializedScriptValueVersion_h
 #define WebSerializedScriptValueVersion_h
 
+#include <cstdint>
+
+#include "third_party/WebKit/public/platform/WebCommon.h"
+
 namespace blink {
 
-// SerializedScriptValue wire format version. Versions higher than
-// this value will not be deserializable by WebSerializedScriptValue.
-// Embedders may serialize this as out-of-band metadata along with
-// collections of serialized data so that version skew can be detected
-// before deserializing individual values.
-const unsigned kSerializedScriptValueVersion = 16;
+// The currently supported version data for serialized script values.
+// This is the version that will be written. Values can be read only if they
+// were written by a serializer for which both |v8_version| and |blink_version|
+// were less than or equal to the current version.
+//
+// Versions higher than |current()| will not be deserializable by
+// WebSerializedScriptValue.  Embedders may serialize this as out-of-band
+// metadata along with collections of serialized data so that version skew can
+// be detected before deserializing individual values.
+//
+// In general, both versions should monotonically increase.
+struct WebSerializedScriptValueVersion {
+  uint32_t v8Version = 0;
+  uint32_t blinkVersion = 0;
+
+  BLINK_EXPORT static WebSerializedScriptValueVersion current();
+};
 
 }  // namespace blink