Event tracing for sync events

Adds a "sync" trace event category that traces the following events:
- model association time
- time spent in each step of the syncer state machine
- transactions

Also included is a "sync_lock_contention" category that tracks the time spent
acquiring the sync lock. This information would normally clutter up the logs,
but it is useful information when we suspect lock contention is an issue.

To trace model association tracing, I needed to have a set of strings with
application lifetime representing each model type.  I have changed the
return type of ModelTypeToString from std::string to const char* to meet this
need.

In the interest of avoiding duplicate functionality, this change also removes
other mechanisms for tracing transaction time. In particular, some of the log
messages around acquiring and releasing transactions have been removed.

BUG=104353
TEST=Run with '--trace-startup=sync,sync_lock_contention', open resulting
chrometrace.log in about:tracing.


Review URL: http://codereview.chromium.org/8573011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111265 0039d316-1c4b-4281-b951-d872f2087c98

0 files changed, 0 insertions, 0 deletions