Move sRGB <-> linear conversion components to their own files.

tests/SRGBTest.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkSRGB.h"
+#include "Test.h"
+#include <math.h>
+
+static uint8_t linear_to_srgb(float l) {
+    return (uint8_t)roundf(sk_linear_to_srgb(Sk4f{l})[0]);
+}
+
+DEF_TEST(sk_linear_to_srgb, r) {
+    // Should map 0 -> 0 and 1 -> 1.
+    REPORTER_ASSERT(r,   0 == linear_to_srgb(0.0f));
+    REPORTER_ASSERT(r, 255 == linear_to_srgb(1.0f));
+
+    // Should be monotonic between 0 and 1.
+    // We don't bother checking denorm values.
+    uint8_t prev = 0;
+    for (float f = FLT_MIN; f <= 1.0f; ) {
+        uint8_t srgb = linear_to_srgb(f);
+
+        REPORTER_ASSERT(r, srgb >= prev);
+        prev = srgb;
+
+        union { float flt; uint32_t bits; } pun = { f };
+        pun.bits++;
+        f = pun.flt;
+    }
+}