Make isolate.h usable without objects-inl.h header.

test/unittests/compiler/js-builtin-reducer-unittest.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-builtin-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/typer.h"
+#include "src/isolate-inl.h"
 #include "test/unittests/compiler/graph-unittest.h"
 #include "test/unittests/compiler/node-test-utils.h"
 #include "testing/gmock-support.h"
 
 using testing::BitEq;
 using testing::Capture;
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 176 matching lines @@
 
       ASSERT_TRUE(r.Changed());
       EXPECT_THAT(r.replacement(), IsTruncateFloat64ToFloat32(p0));
     }
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8