Add some DVLOG's in MetadataDatabase::Update* methods

BUG=none
TEST=manual

Review URL: https://codereview.chromium.org/101743002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238395 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238395