Add Origin Trials Test interface, rather than attaching trials directly to internals.

third_party/WebKit/Source/core/testing/OriginTrialsTestPartial.h

+// 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 OriginTrialsTestPartial_h
+#define OriginTrialsTestPartial_h
+
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+class OriginTrialsTest;
+
+// This interface is used for testing that partial interfaces can  extend other
+// interfaces at run-time, if the origin trial is enabled.
+class OriginTrialsTestPartial final {
+    STATIC_ONLY(OriginTrialsTestPartial);
+public:
+    static bool normalAttributePartial(OriginTrialsTest&) { return true; }
+    static bool staticAttributePartial() { return true; }
+    static bool methodPartial(OriginTrialsTest&) { return true; }
+    static bool staticMethodPartial() { return true; }
+    static const unsigned kConstantPartial = 2;
+};
+
+} // namespace blink
+
+#endif // OriginTrialsTestPartial_h