Fix timestamp calculation

Windows MIDI API specifies timestamps in milliseconds for MIM_DATA and MIM_LONGDATA.

BUG=329964

Review URL: https://codereview.chromium.org/112403003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242252 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242252