Add field-initializing constructors to generated mojo structs.

mojo/public/cpp/bindings/tests/pickled_types_blink.h

Index: mojo/public/cpp/bindings/tests/pickled_types_blink.h
diff --git a/mojo/public/cpp/bindings/tests/pickled_types_blink.h b/mojo/public/cpp/bindings/tests/pickled_types_blink.h
index 0b7bd20703873fc3539d9b4d911cdaf049e573a2..37e9e70578d82c4c72fd8a607a795f9bb9199f92 100644
--- a/mojo/public/cpp/bindings/tests/pickled_types_blink.h
+++ b/mojo/public/cpp/bindings/tests/pickled_types_blink.h
@@ -51,9 +51,14 @@ class PickledStructBlink {
     bar_ = bar;
   }
 
+  // The |baz| field should never be serialized.
+  int baz() const { return baz_; }
+  void set_baz(int baz) { baz_ = baz; }
+
  private:
   int foo_ = 0;
   int bar_ = 0;
+  int baz_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(PickledStructBlink);
 };