Use signaling NaN for holes in fixed double arrays.

src/base/math.h

Index: src/base/math.h
diff --git a/src/base/math.h b/src/base/math.h
new file mode 100644
index 0000000000000000000000000000000000000000..ef8612177846151a13195c1fc9133d6e1e2adfab
--- /dev/null
+++ b/src/base/math.h
@@ -0,0 +1,19 @@
+// Copyright 2015 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.
+
+#ifndef V8_BASE_MATH_H_
+#define V8_BASE_MATH_H_
+
+namespace v8 {
+namespace base {
+
+bool IsQuietNaN(float x);
+bool IsQuietNaN(double x);
+bool IsSignalingNaN(float x);
+bool IsSignalingNaN(double x);
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_MATH_H_