Initialize primitive type classes during linker initialization.

Change-Id: Ib31da85afcc59c5d0a14346fb7f97043487fd662
diff --git a/src/object.cc b/src/object.cc
index a380b5a..7c28d76 100644
--- a/src/object.cc
+++ b/src/object.cc
@@ -57,7 +57,7 @@
 uint32_t Method::NumArgRegisters() {
   CHECK(shorty_ != NULL);
   uint32_t num_registers = 0;
-  for (size_t i = 1; shorty_[i] != '\0'; ++i) {
+  for (int i = 1; i < shorty_.length(); ++i) {
     char ch = shorty_[i];
     if (ch == 'D' || ch == 'J') {
       num_registers += 2;