Add helpers for logging mojom objects.

mojo/public/cpp/bindings/struct_ptr.h

Index: mojo/public/cpp/bindings/struct_ptr.h
diff --git a/mojo/public/cpp/bindings/struct_ptr.h b/mojo/public/cpp/bindings/struct_ptr.h
index 1b34a9ec036149c229d63d1f4a139ceb8de96093..1bfc0ed85b5484dddccf7bb5528bc9e704407a0b 100644
--- a/mojo/public/cpp/bindings/struct_ptr.h
+++ b/mojo/public/cpp/bindings/struct_ptr.h
@@ -6,6 +6,7 @@
 #define MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_
 
 #include <cstddef>
+#include <iosfwd>
 #include <memory>
 #include <new>
 
@@ -127,7 +128,7 @@ class InlinedStructPtr {
 
   void reset() {
     is_null_ = true;
-    value_. ~Struct();
+    value_.~Struct();
     new (&value_) Struct();
   }
 
@@ -175,6 +176,22 @@ class InlinedStructPtr {
   MOJO_MOVE_ONLY_TYPE(InlinedStructPtr);
 };
 
+// Prints the pointee of a Mojo structure pointer to an output stream
+// for debugging purposes, assuming there exists an operator<< overload
+// that accepts a const reference to the object.
+template <typename T, typename = typename T::Data_>
+auto operator<<(std::ostream& os, const T* value) -> decltype(os << *value) {
+  return value ? os << *value : os << "null";
+}
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const StructPtr<T>& value) {
+  return os << value.get();
+}
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const InlinedStructPtr<T>& value) {
+  return os << value.get();
+}
+
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_