Implement a simple ThreadChecker for Mojo and add to |internal::SharedData| and |internal::Router|.

third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h

Index: third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h
diff --git a/third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h b/third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h
index 54c9346fc98539eaea8569ab1669a99c66dd0e1d..2676224c82e0ca0044de55d73d131ef167c2f940 100644
--- a/third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h
+++ b/third_party/mojo/src/mojo/public/cpp/bindings/lib/shared_data.h
@@ -5,6 +5,9 @@
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_SHARED_DATA_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SHARED_DATA_H_
 
+#include <assert.h>
+
+#include "mojo/public/cpp/bindings/lib/thread_checker.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
@@ -53,8 +56,12 @@ class SharedData {
     Holder() : value(), ref_count_(1) {}
     Holder(const T& value) : value(value), ref_count_(1) {}
 
-    void Retain() { ++ref_count_; }
+    void Retain() {
+      assert(thread_checker_.CalledOnValidThread());
+      ++ref_count_;
+    }
     void Release() {
+      assert(thread_checker_.CalledOnValidThread());
       if (--ref_count_ == 0)
         delete this;
     }
@@ -63,6 +70,7 @@ class SharedData {
 
    private:
     int ref_count_;
+    ThreadChecker thread_checker_;
     MOJO_DISALLOW_COPY_AND_ASSIGN(Holder);
   };