Add support for unresolved classes in optimizing.

Change-Id: I0e299a81e560eb9cb0737ec46125dffc99333b54
diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 3287a0a..86a3ad9 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -216,7 +216,11 @@
   }
 
   ReferenceTypeInfo class_rti = klass->GetLoadedClassRTI();
-  DCHECK(class_rti.IsValid() && class_rti.IsExact());
+  if (!class_rti.IsValid()) {
+    // Happens when the loaded class is unresolved.
+    return false;
+  }
+  DCHECK(class_rti.IsExact());
   if (class_rti.IsSupertypeOf(obj_rti)) {
     *outcome = true;
     return true;