Replace forward declarations with includes in TaskRunner APIs.

base/task_runner.h

Index: base/task_runner.h
diff --git a/base/task_runner.h b/base/task_runner.h
index 6dd82ccaca999b41535c79e4a6968e1c939ef43e..9593835eebbdfa51f43e1d236f387f3ee1ac7940 100644
--- a/base/task_runner.h
+++ b/base/task_runner.h
@@ -9,13 +9,10 @@
 
 #include "base/base_export.h"
 #include "base/callback_forward.h"
+#include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 
-namespace tracked_objects {
-class Location;
-} // namespace tracked_objects
-
 namespace base {
 
 struct TaskRunnerTraits;