Add message sizing to basic IPC traits and struct macros.

base/files/file_path.cc

Index: base/files/file_path.cc
diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index 63e93879a3575dc426990af51775f41198edf92e..8cb2ebc69d2f6a3e1d9a6f99ece03e13881635e8 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -657,6 +657,14 @@ FilePath FilePath::FromUTF16Unsafe(const string16& utf16) {
 }
 #endif
 
+void FilePath::GetSizeForPickle(PickleSizer* sizer) const {
+#if defined(OS_WIN)
+  sizer->AddString16(path_);
+#else
+  sizer->AddString(path_);
+#endif
+}
+
 void FilePath::WriteToPickle(Pickle* pickle) const {
 #if defined(OS_WIN)
   pickle->WriteString16(path_);