Make singleton SkColorSpaces thread safe

tests/ColorSpaceTest.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 "Resources.h"
 #include "SkCodec.h"
 #include "SkColorSpace.h"
 #include "SkColorSpace_Base.h"
 #include "Test.h"
 
 #include "png.h"
 
 static bool almost_equal(float a, float b) {
     return SkTAbs(a - b) < 0.001f;
 }
 
 static void test_space(skiatest::Reporter* r, SkColorSpace* space,
                        const float red[], const float green[], const float blue[],
                        const SkColorSpace::GammaNamed expectedGamma) {
 
     REPORTER_ASSERT(r, expectedGamma == space->gammaNamed());
 
 
-    SkMatrix44 mat = space->xyz();
+    const SkMatrix44& mat = space->xyz();
     const float src[] = {
         1, 0, 0, 1,
         0, 1, 0, 1,
         0, 0, 1, 1,
     };
     float dst[4];
     for (int i = 0; i < 3; ++i) {
         mat.mapScalars(&src[i*4], dst);
         REPORTER_ASSERT(r, almost_equal(red[i],   dst[0]));
         REPORTER_ASSERT(r, almost_equal(green[i], dst[1]));
@@ skipping 214 matching lines @@
     REPORTER_ASSERT(r, !SkColorSpace::Equals(nullptr, srgb.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(srgb.get(), nullptr));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(adobe.get(), srgb.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(z30.get(), srgb.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(z32.get(), z30.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(upperLeft.get(), srgb.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(upperLeft.get(), upperRight.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(z30.get(), upperRight.get()));
     REPORTER_ASSERT(r, !SkColorSpace::Equals(upperRight.get(), adobe.get()));
 }