Create FP16 LUTs when needed

ui/gfx/half_float.h

+// Copyright (c) 2017 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 UI_GFX_COLOR_HALF_FLOAT_H_
+#define UI_GFX_COLOR_HALF_FLOAT_H_
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+typedef uint16_t HalfFloat;
+
+// Floats are expected to be within +/- 65535.0;
+GFX_EXPORT void FloatToHalfFloat(const float* input,
+                                 HalfFloat* output,
+                                 size_t num);
+};
+#endif