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

third_party/WebKit/public/web/WebSerializedScriptValueVersion.h

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #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;

[cmumford, 2017/04/05 21:23:18]

v8 has a major and minor version (V8_MAJOR_VERSION & V8_MINOR_VERSION). How will
they map to v8Version?

[jbroman, 2017/04/05 21:27:10]

V8 has a wire format version, which is analogous to Blink's. I recently exposed
it as v8::ValueSerializer::GetCurrentDataFormatVersion(), though that's only
available at runtime, so it'd have to move to be a header constant to satisfy
the concerns you and dcheng have.

The V8 published version number has to do with the V8 release process, and isn't
great for this purpose. (Similarly, we don't use the Chromium
milestone.minor.branch.patch version for the Blink-side versioning.)

+  uint32_t blinkVersion = 0;
+
+  BLINK_EXPORT static WebSerializedScriptValueVersion current();
+};
 
 }  // namespace blink
 
 #endif  // WebSerializedScriptValueVersion_h