Allowing V8ObjectStatsMetric users to specify metrics to capture.

V8ObjectStatsMetric would previously capture all V8 statistics.
Added a constructor parameter so that users could capture a subset
of the V8 statistics if desired. Default is as before: capture them
all.

Making this change so that the IndexedDB perf tests (indexeddb_perf)
can be modified to report only a few metrics to simplify the test
results.

Review URL: https://codereview.chromium.org/99903009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243394 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243394