Make mojom-generated C++ string constants really constant.

mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 {%- if variant -%}
 {%-   set variant_path = "%s-%s"|format(module.path, variant) -%}
 {%- else -%}
 {%-   set variant_path = module.path -%}
 {%- endif %}
 
@@ skipping 32 matching lines @@
 
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
 {%- if variant %}
 namespace {{variant}} {
 {%- endif %}
 
 {#--- Constants #}
 {%- for constant in module.constants %}
-{%-   if not constant.kind|is_integral_kind %}
-const {{constant.kind|cpp_pod_type}} {{constant.name}} = {{constant|constant_value}};
+{%-   if constant.kind|is_string_kind %}
+const char {{constant.name}}[] = {{constant|constant_value}};
 {%-   endif %}
 {%- endfor %}
 
 {#--- Struct Constants #}
 {%- for struct in structs %}
 {%-   for constant in struct.constants %}
-{%-     if constant.kind|is_integral_kind %}
-const {{constant.kind|cpp_pod_type}} {{struct.name}}::{{constant.name}};
-{%-     else %}
-const {{constant.kind|cpp_pod_type}} {{struct.name}}::{{constant.name}} = {{constant|constant_value}};
+{%-     if constant.kind|is_string_kind %}
+const char {{struct.name}}::{{constant.name}}[] = {{constant|constant_value}};
 {%-     endif %}
 {%-   endfor %}
 {%- endfor %}
 
 {#--- Struct builder definitions #}
 {%- for struct in structs %}
 {%-   if not struct|is_native_only_kind %}
 {%-     include "wrapper_class_definition.tmpl" %}
 {%-   endif %}
 {%- endfor %}
@@ skipping 29 matching lines @@
 {%-   include "union_traits_definition.tmpl" %}
 {%- endfor %}
 
 }  // namespace mojo
 
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #elif defined(_MSC_VER)
 #pragma warning(pop)
 #endif