Fix mutation fuzzing bindings for structs and unions.

Add missing argument to mutateStruct/Union calls.

Bug: 607649
Change-Id: Ie2a3732e3295ac513a9c0ca6f4a3d5742a58cc63
Reviewed-on: https://chromium-review.googlesource.com/1077874Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Oliver Chang <ochang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563150}

mojo/public/tools/bindings/generators/js_templates/fuzzing.tmpl

@@ -114,9 +114,9 @@ idx = {{name}}.setHandlesInternal_(handles, idx)
 {%-   elif kind|is_enum_kind -%}
 {{generate_or_mutate_enum(obj, operation, kind, name)}}
 {%-   elif kind|is_struct_kind -%}
-{{build_call(obj, operation, 'Struct', kind.module.namespace ~ '.' ~ kind.name, kind.is_nullable|to_js_boolean)}}
+{{build_call(obj, operation, 'Struct', name, kind.module.namespace ~ '.' ~ kind.name, kind.is_nullable|to_js_boolean)}}
 {%-   elif kind|is_union_kind -%}
-{{build_call(obj, operation, 'Union', kind.module.namespace ~ '.' ~ kind.name, kind.is_nullable|to_js_boolean)}}
+{{build_call(obj, operation, 'Union', name, kind.module.namespace ~ '.' ~ kind.name, kind.is_nullable|to_js_boolean)}}
 {%-   elif kind|is_array_kind -%}
 {{generate_or_mutate_array(obj, operation, kind, name)}}
 {%-   elif kind|is_map_kind -%}

mojo/public/tools/bindings/generators/js_templates/union_definition.tmpl

@@ -64,7 +64,7 @@ function {{union.name}}(value) {
     {
       field: "{{field.name}}",
 
-      mutator: function() { return {{generate_or_mutate('mutator_', 'mutate', field.kind, 'this.' ~ field.name)|indent(6)}}; },
+      mutator: function(val) { return {{generate_or_mutate('mutator_', 'mutate', field.kind, 'val.' ~ field.name)|indent(6)}}; },
     },
 {%-     endfor %}
   ];