Add array traits for WTF::Vector.

mojo/public/cpp/bindings/array_traits_wtf_vector.h

Index: mojo/public/cpp/bindings/array_traits_wtf_vector.h
diff --git a/mojo/public/cpp/bindings/array_traits_wtf_vector.h b/mojo/public/cpp/bindings/array_traits_wtf_vector.h
new file mode 100644
index 0000000000000000000000000000000000000000..9b3755ad4f161be04e67371a140b9da80a8d8f39
--- /dev/null
+++ b/mojo/public/cpp/bindings/array_traits_wtf_vector.h
@@ -0,0 +1,44 @@
+// Copyright 2016 The Chromium 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 MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_WTF_VECTOR_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_WTF_VECTOR_H_
+
+#include "mojo/public/cpp/bindings/array_traits.h"
+#include "third_party/WebKit/Source/wtf/Vector.h"
+
+namespace mojo {
+
+template <typename U>
+struct ArrayTraits<WTF::Vector<U>> {
+  using Element = U;
+
+  static bool IsNull(const WTF::Vector<U>& input) {
+    // WTF::Vector<> is always converted to non-null mojom array.
+    return false;
+  }
+
+  static void SetToNull(WTF::Vector<U>* output) {
+    // WTF::Vector<> doesn't support null state. Set it to empty instead.
+    output->clear();
+  }
+
+  static size_t GetSize(const WTF::Vector<U>& input) { return input.size(); }
+
+  static U* GetData(WTF::Vector<U>& input) { return input.data(); }
+
+  static const U* GetData(const WTF::Vector<U>& input) { return input.data(); }
+
+  static U& GetAt(WTF::Vector<U>& input, size_t index) { return input[index]; }
+
+  static const U& GetAt(const WTF::Vector<U>& input, size_t index) {
+    return input[index];
+  }
+
+  static void Resize(WTF::Vector<U>& input, size_t size) { input.resize(size); }
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_WTF_VECTOR_H_