Fix class_linker_test now FindClass uses const char*.

Also move FindSystemClass into the .cc file, where it belongs.

Change-Id: I171555ad6cf408be926b3f99ea61e2c5a835d1ec
diff --git a/src/class_linker.h b/src/class_linker.h
index 6feacc0..d735515 100644
--- a/src/class_linker.h
+++ b/src/class_linker.h
@@ -57,9 +57,7 @@
   // If class_loader is null, searches boot_class_path_.
   Class* FindClass(const char* descriptor, const ClassLoader* class_loader);
 
-  Class* FindSystemClass(const char* descriptor) {
-    return FindClass(descriptor, NULL);
-  }
+  Class* FindSystemClass(const char* descriptor);
 
   // Define a new a class based on a ClassDef from a DexFile
   Class* DefineClass(const StringPiece& descriptor, const ClassLoader* class_loader,