Add field-initializing constructors to generated mojo structs.

mojo/public/cpp/bindings/lib/native_struct.cc

Index: mojo/public/cpp/bindings/lib/native_struct.cc
diff --git a/mojo/public/cpp/bindings/lib/native_struct.cc b/mojo/public/cpp/bindings/lib/native_struct.cc
index 3c3c2c37f0436e66466c07f669b1006aca6881a2..7b1a1a6c594f6429cd58bdd7aecd537c1bd68f26 100644
--- a/mojo/public/cpp/bindings/lib/native_struct.cc
+++ b/mojo/public/cpp/bindings/lib/native_struct.cc
@@ -10,9 +10,7 @@ namespace mojo {
 
 // static
 NativeStructPtr NativeStruct::New() {
-  NativeStructPtr rv;
-  internal::StructHelper<NativeStruct>::Initialize(&rv);
-  return rv;
+  return NativeStructPtr(base::in_place);
 }
 
 NativeStruct::NativeStruct() {}