Fix HCheckValue::Canonicalize wrt uninitialized HConstant unique.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index f7a3554f7ae8350418f3cbf4c3849d254d0a455f..52c31b3de54a34195a4b616bc05ff65e9928749c 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3541,6 +3541,10 @@ class HConstant V8_FINAL : public HTemplateInstruction<0> {
     return object_;
   }
 
+  bool EqualsUnique(Unique<Object> other) const {
+    return object_.IsInitialized() && object_ == other;
+  }
+
 #ifdef DEBUG
   virtual void Verify() V8_OVERRIDE { }
 #endif