Use VM type cast and save handles.

runtime/vm/dart_entry_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/object.h"
@@ skipping 50 matching lines @@
       lib.LookupClass(String::Handle(String::NewSymbol("A"))));
   EXPECT(!cls.IsNull());
   String& name = String::Handle(String::New("foo"));
   Function& function = Function::Handle(cls.LookupStaticFunction(name));
   EXPECT(!function.IsNull());
   GrowableArray<const Object*> arguments;
   const Array& kNoArgumentNames = Array::Handle();
   const Object& retval = Object::Handle(
       DartEntry::InvokeStatic(function, arguments, kNoArgumentNames));
   EXPECT(retval.IsError());
-  Error& error = Error::Handle();
-  error ^= retval.raw();
-  EXPECT_SUBSTRING("++++", error.ToErrorCString());
+  EXPECT_SUBSTRING("++++", Error::Cast(retval).ToErrorCString());
 }
 
 
 TEST_CASE(InvokeDynamic_CompileError) {
   const char* kScriptChars =
       "class A {\n"
       "  foo() { return ++++; }\n"
       "}\n";
   String& url = String::Handle(String::New("dart-test:DartEntry"));
   String& source = String::Handle(String::New(kScriptChars));
@@ skipping 19 matching lines @@
 
   // Call foo.
   String& name = String::Handle(String::New("foo"));
   Function& function = Function::Handle(cls.LookupDynamicFunction(name));
   EXPECT(!function.IsNull());
   GrowableArray<const Object*> arguments;
   const Object& retval = Object::Handle(
       DartEntry::InvokeDynamic(
           instance, function, arguments, kNoArgumentNames));
   EXPECT(retval.IsError());
-  Error& error = Error::Handle();
-  error ^= retval.raw();
-  EXPECT_SUBSTRING("++++", error.ToErrorCString());
+  EXPECT_SUBSTRING("++++", Error::Cast(retval).ToErrorCString());
 }
 
 #endif  // TARGET_ARCH_IA32 || TARGET_ARCH_X64.
 
 }  // namespace dart