Generate param traits size methods for IPC files in content/ (and traits it depends on).

base/pickle.cc

Index: base/pickle.cc
diff --git a/base/pickle.cc b/base/pickle.cc
index 94f3b1c9a13ac05700fb56638559074bb10f0c0e..cfb316c13e56974abc7ffb98fa7e4693e40a7301 100644
--- a/base/pickle.cc
+++ b/base/pickle.cc
@@ -231,6 +231,12 @@ void PickleSizer::AddBytes(int length) {
   payload_size_ += bits::Align(length, sizeof(uint32_t));
 }
 
+void PickleSizer::AddAttachment() {
+  // From IPC::Message::WriteAttachment
+  AddBool();
+  AddInt();
+}
+
 template <size_t length> void PickleSizer::AddBytesStatic() {
   DCHECK_LE(length, static_cast<size_t>(std::numeric_limits<int>::max()));
   AddBytes(length);