Throw if ResolveMethod fails.

It's impractical for the lower-level Find*Method calls to throw because
they're used in class initialization and exception throwing.

Change-Id: Idece1ea99553a758ebc23d987e46b59f0445ea67
diff --git a/src/object.cc b/src/object.cc
index 5017c23..0e8e176 100644
--- a/src/object.cc
+++ b/src/object.cc
@@ -1139,9 +1139,9 @@
 }
 
 Method* Class::FindVirtualMethod(const StringPiece& name,
-                                 const StringPiece& descriptor) {
+                                 const StringPiece& signature) {
   for (Class* klass = this; klass != NULL; klass = klass->GetSuperClass()) {
-    Method* method = klass->FindDeclaredVirtualMethod(name, descriptor);
+    Method* method = klass->FindDeclaredVirtualMethod(name, signature);
     if (method != NULL) {
       return method;
     }