[Tracing] Add support for forward looking or backwards looking async steps.

Renamed TRACE_EVENT_ASYNC_STEP to TRACE_EVENT_ASYNC_STEP_INTO and
added TRACE_EVENT_ASYNC_STEP_PAST. These are mutually exclusive. Users
must decide all of their steps are backwards or forwards looking for an
async event.

Updated callers to use the correct versions. Note that we had both!

BUG=None
TBR=nduca,mmenke,wjia,hclam

Review URL: https://codereview.chromium.org/25536014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230606 0039d316-1c4b-4281-b951-d872f2087c98
Add media_perftests target.

BUG=310837

Review URL: https://codereview.chromium.org/38403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230607 0039d316-1c4b-4281-b951-d872f2087c98
Clean up HistoryURLProvider by removing test related data.

BUG=None

Review URL: https://codereview.chromium.org/38613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230608 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230608