mojo: Mark DataView readers as WARN_UNUSED_RESULT.

mojo/public/tools/bindings/generators/cpp_templates/struct_data_view_declaration.tmpl

 class {{struct.name}}DataView {
  public:
   {{struct.name}}DataView() {}
 
   {{struct.name}}DataView(
       internal::{{struct.name}}_Data* data,
       mojo::internal::SerializationContext* context)
 {%- if struct|requires_context_for_data_view %}
       : data_(data), context_(context) {}
 {%- else %}
       : data_(data) {}
 {%- endif %}
 
   bool is_null() const { return !data_; }
 
 {%- for pf in struct.packed.packed_fields_in_ordinal_order %}
 {%-   set kind = pf.field.kind %}
 {%-   set name = pf.field.name %}
 {%-   if kind|is_union_kind %}
   inline void Get{{name|under_to_camel}}DataView(
       {{kind|cpp_data_view_type}}* output);
 
   template <typename UserType>
-  bool Read{{name|under_to_camel}}(UserType* output) {
+  WARN_UNUSED_RESULT bool Read{{name|under_to_camel}}(UserType* output) {
 {%-     if pf.min_version != 0 %}
-    auto pointer = data_->header_.version >= {{pf.min_version}}
-                   ? &data_->{{name}} : nullptr;
+    auto* pointer = data_->header_.version >= {{pf.min_version}}
+                    ? &data_->{{name}} : nullptr;
 {%-     else %}
-    auto pointer = &data_->{{name}};
+    auto* pointer = &data_->{{name}};
 {%-     endif %}
     return mojo::internal::Deserialize<{{kind|unmapped_type_for_serializer}}>(
         pointer, output, context_);
   }
 
 {%-   elif kind|is_object_kind %}
   inline void Get{{name|under_to_camel}}DataView(
       {{kind|cpp_data_view_type}}* output);
 
   template <typename UserType>
-  bool Read{{name|under_to_camel}}(UserType* output) {
+  WARN_UNUSED_RESULT bool Read{{name|under_to_camel}}(UserType* output) {
 {%-     if pf.min_version != 0 %}
-    auto pointer = data_->header_.version >= {{pf.min_version}}
-                   ? data_->{{name}}.Get() : nullptr;
+    auto* pointer = data_->header_.version >= {{pf.min_version}}
+                    ? data_->{{name}}.Get() : nullptr;
 {%-     else %}
-    auto pointer = data_->{{name}}.Get();
+    auto* pointer = data_->{{name}}.Get();
 {%-     endif %}
     return mojo::internal::Deserialize<{{kind|unmapped_type_for_serializer}}>(
         pointer, output, context_);
   }
 
 {%-   elif kind|is_enum_kind %}
   template <typename UserType>
-  bool Read{{name|under_to_camel}}(UserType* output) const {
+  WARN_UNUSED_RESULT bool Read{{name|under_to_camel}}(UserType* output) const {
 {%-     if pf.min_version != 0 %}
     auto data_value = data_->header_.version >= {{pf.min_version}}
                       ? data_->{{name}} : 0;
 {%-     else %}
     auto data_value = data_->{{name}};
 {%-     endif %}
     return mojo::internal::Deserialize<{{kind|unmapped_type_for_serializer}}>(
         data_value, output);
   }
 
@@ skipping 45 matching lines @@
 
 {%-   endif %}
 {%- endfor %}
  private:
   internal::{{struct.name}}_Data* data_ = nullptr;
 {%- if struct|requires_context_for_data_view %}
   mojo::internal::SerializationContext* context_ = nullptr;
 {%- endif %}
 };