Add FlushForTesting to InterfacePtr and Binding.

mojo/public/cpp/bindings/binding_set.h

Index: mojo/public/cpp/bindings/binding_set.h
diff --git a/mojo/public/cpp/bindings/binding_set.h b/mojo/public/cpp/bindings/binding_set.h
index dc66860b4e0d78fba19a3de4727f59bb6e235a59..69f17cc0f1cf1ecb0ec4e58e38d8952586e52511 100644
--- a/mojo/public/cpp/bindings/binding_set.h
+++ b/mojo/public/cpp/bindings/binding_set.h
@@ -95,6 +95,12 @@ class BindingSet {
     return dispatch_context_;
   }
 
+  void FlushForTesting() {
+    for (auto& binding : bindings_) {
+      binding.first->FlushForTesting();
+    }
+  }
+
  private:
   friend class Entry;
 
@@ -113,6 +119,8 @@ class BindingSet {
           &Entry::OnConnectionError, base::Unretained(this)));
     }
 
+    void FlushForTesting() { binding_.FlushForTesting(); }
+
    private:
     class DispatchFilter : public MessageReceiver {
      public: