Move CancelableTaskTracker to //base/task/CancelableTaskTracker.

chrome/browser/sessions/session_service.cc

Index: chrome/browser/sessions/session_service.cc
diff --git a/chrome/browser/sessions/session_service.cc b/chrome/browser/sessions/session_service.cc
index 5655a97efea3432c94739600ca84cbdbee5ecd31..d2b0967f744df9f0d81c6f6b7cb6250a73a18cd1 100644
--- a/chrome/browser/sessions/session_service.cc
+++ b/chrome/browser/sessions/session_service.cc
@@ -497,9 +497,9 @@ void SessionService::SetTabUserAgentOverride(
       kCommandSetTabUserAgentOverride, tab_id.id(), user_agent_override));
 }
 
-CancelableTaskTracker::TaskId SessionService::GetLastSession(
+base::CancelableTaskTracker::TaskId SessionService::GetLastSession(
     const SessionCallback& callback,
-    CancelableTaskTracker* tracker) {
+    base::CancelableTaskTracker* tracker) {
   // OnGotSessionCommands maps the SessionCommands to browser state, then run
   // the callback.
   return ScheduleGetLastSessionCommands(