Add thread checker to StatsCollection.

talk/app/webrtc/statstypes.h

Index: talk/app/webrtc/statstypes.h
diff --git a/talk/app/webrtc/statstypes.h b/talk/app/webrtc/statstypes.h
index c58f39058b152b820552d3ad805641de4d4a56cc..156e784acfd04cf06653132092590703781f0e2c 100644
--- a/talk/app/webrtc/statstypes.h
+++ b/talk/app/webrtc/statstypes.h
@@ -43,6 +43,7 @@
 #include "webrtc/base/linked_ptr.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/stringencode.h"
+#include "webrtc/base/thread_checker.h"
 
 namespace webrtc {
 
@@ -383,7 +384,6 @@ typedef std::vector<const StatsReport*> StatsReports;
 // A map from the report id to the report.
 // This class wraps an STL container and provides a limited set of
 // functionality in order to keep things simple.
-// TODO(tommi): Use a thread checker here (currently not in libjingle).
 class StatsCollection {
  public:
   StatsCollection();
@@ -409,6 +409,7 @@ class StatsCollection {
 
  private:
   Container list_;
+  rtc::ThreadChecker thread_checker_;
 };
 
 }  // namespace webrtc