[Draft] try out the idea of adding export macros for C++ bindings.

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

 # 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.
 
 """Generates C++ source files from a mojom.Module."""
 
 import mojom.generate.generator as generator
 import mojom.generate.module as mojom
 import mojom.generate.pack as pack
 from mojom.generate.template_expander import UseJinja
@@ skipping 457 matching lines @@
     "passes_associated_kinds": mojom.PassesAssociatedKinds,
     "struct_size": lambda ps: ps.GetTotalSize() + _HEADER_SIZE,
     "stylize_method": generator.StudlyCapsToCamel,
     "under_to_camel": generator.UnderToCamel,
   }
 
   def GetExtraHeaders(self):
     extra_headers = set()
     for name, entry in self.typemap.iteritems():
       extra_headers.update(entry["headers"])
+    if self.dll_export_include:
+      extra_headers.add(self.dll_export_include)
     return list(extra_headers)
 
   def GetJinjaExports(self):
     return {
       "module": self.module,
       "namespace": self.module.namespace,
       "namespaces_as_array": NamespaceToArray(self.module.namespace),
       "imports": self.module.imports,
       "kinds": self.module.kinds,
       "enums": self.module.enums,
       "structs": self.GetStructs(),
       "unions": self.GetUnions(),
       "interfaces": self.GetInterfaces(),
       "variant": self.variant,
       "extra_headers": self.GetExtraHeaders(),
+      "dll_export": self.dll_export_declaration,
     }
 
   @staticmethod
   def GetTemplatePrefix():
     return "cpp_templates"
 
   @classmethod
   def GetFilters(cls):
     return cls.cpp_filters
 
@@ skipping 12 matching lines @@
   def GenerateFiles(self, args):
     global _current_typemap
     _current_typemap = self.typemap
     suffix = "-%s" % self.variant if self.variant else ""
     self.Write(self.GenerateModuleHeader(),
         self.MatchMojomFilePath("%s%s.h" % (self.module.name, suffix)))
     self.Write(self.GenerateModuleInternalHeader(),
         self.MatchMojomFilePath("%s%s-internal.h" % (self.module.name, suffix)))
     self.Write(self.GenerateModuleSource(),
         self.MatchMojomFilePath("%s%s.cc" % (self.module.name, suffix)))