Mojo typemap config: support "copyable_pass_by_value" attribute.

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 209 matching lines @@
   if mojom.IsStructKind(kind) or mojom.IsUnionKind(kind):
     return True
   if mojom.IsArrayKind(kind):
     return IsMoveOnlyKind(kind.kind) if _use_new_wrapper_types else True
   if mojom.IsMapKind(kind):
     return IsMoveOnlyKind(kind.value_kind) if _use_new_wrapper_types else True
   if mojom.IsAnyHandleOrInterfaceKind(kind):
     return True
   return False
 
+def IsCopyablePassByValue(kind):
+  if not IsTypemappedKind(kind):
+    return False
+  return _current_typemap[GetFullMojomNameForKind(kind)][
+      "copyable_pass_by_value"]
+
 def ShouldPassParamByValue(kind):
-  return (not mojom.IsReferenceKind(kind)) or IsMoveOnlyKind(kind)
+  return ((not mojom.IsReferenceKind(kind)) or IsMoveOnlyKind(kind) or
+      IsCopyablePassByValue(kind))
 
 def GetCppWrapperParamType(kind):
   cpp_wrapper_type = GetCppWrapperType(kind)
   return (cpp_wrapper_type if ShouldPassParamByValue(kind)
                            else "const %s&" % cpp_wrapper_type)
 
 def GetCppFieldType(kind):
   if mojom.IsStructKind(kind):
     return ("mojo::internal::Pointer<%s>" %
         GetNameForKind(kind, internal=True))
@@ skipping 258 matching lines @@
     _use_new_wrapper_types = self.use_new_wrapper_types
     global _variant
     _variant = self.variant
     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)))