color: Clarify default behaviors

ui/gfx/color_transform_unittest.cc

 // Copyright (c) 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.
 
 #include "base/logging.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/color_space.h"
 #include "ui/gfx/color_transform.h"
 #include "ui/gfx/icc_profile.h"
 #include "ui/gfx/test/icc_profiles.h"
@@ skipping 176 matching lines @@
   EXPECT_NEAR(tmp.y(), 1.0f, kEpsilon);
   EXPECT_NEAR(tmp.z(), 0.0f, kEpsilon);
 
   tmp = ColorTransform::TriStim(0.0f, 0.0f, 1.0f);
   t->Transform(&tmp, 1);
   EXPECT_NEAR(tmp.x(), 0.0f, kEpsilon);
   EXPECT_NEAR(tmp.y(), 0.0f, kEpsilon);
   EXPECT_NEAR(tmp.z(), 1.0f, kEpsilon);
 }
 
-TEST(SimpleColorSpace, UnknownToSRGB) {
-  ColorSpace unknown;
+TEST(SimpleColorSpace, UnknownVideoToSRGB) {
+  // Invalid video spaces should be BT709.
+  ColorSpace unknown = gfx::ColorSpace::CreateVideo(
+      -1, -1, -1, gfx::ColorSpace::RangeID::LIMITED);
   ColorSpace sRGB = ColorSpace::CreateSRGB();
   std::unique_ptr<ColorTransform> t(ColorTransform::NewColorTransform(
       unknown, sRGB, ColorTransform::Intent::INTENT_PERCEPTUAL));
 
   ColorTransform::TriStim tmp(16.0f / 255.0f, 0.5f, 0.5f);
   t->Transform(&tmp, 1);
   EXPECT_NEAR(tmp.x(), 0.0f, 0.001f);
   EXPECT_NEAR(tmp.y(), 0.0f, 0.001f);
   EXPECT_NEAR(tmp.z(), 0.0f, 0.001f);
 
   tmp = ColorTransform::TriStim(235.0f / 255.0f, 0.5f, 0.5f);
   t->Transform(&tmp, 1);
   EXPECT_NEAR(tmp.x(), 1.0f, 0.001f);
   EXPECT_NEAR(tmp.y(), 1.0f, 0.001f);
   EXPECT_NEAR(tmp.z(), 1.0f, 0.001f);
 
   // Test a blue color
   tmp = ColorTransform::TriStim(128.0f / 255.0f, 240.0f / 255.0f, 0.5f);
   t->Transform(&tmp, 1);
   EXPECT_GT(tmp.z(), tmp.x());
   EXPECT_GT(tmp.z(), tmp.y());
 }
 
+TEST(SimpleColorSpace, DefaultToSRGB) {
+  // The default value should do no transformation, regardless of destination.
+  ColorSpace unknown;
+  std::unique_ptr<ColorTransform> t1(ColorTransform::NewColorTransform(
+      unknown, ColorSpace::CreateSRGB(),
+      ColorTransform::Intent::INTENT_PERCEPTUAL));
+  EXPECT_EQ(t1->NumberOfStepsForTesting(), 0u);
+  std::unique_ptr<ColorTransform> t2(ColorTransform::NewColorTransform(
+      unknown, ColorSpace::CreateXYZD50(),
+      ColorTransform::Intent::INTENT_PERCEPTUAL));
+  EXPECT_EQ(t2->NumberOfStepsForTesting(), 0u);
+}
+
 class TransferTest : public testing::TestWithParam<ColorSpace::TransferID> {};
 
 TEST_P(TransferTest, basicTest) {
   gfx::ColorSpace space_with_transfer(ColorSpace::PrimaryID::BT709, GetParam(),
                                       ColorSpace::MatrixID::RGB,
                                       ColorSpace::RangeID::FULL);
   gfx::ColorSpace space_linear(
       ColorSpace::PrimaryID::BT709, ColorSpace::TransferID::LINEAR,
       ColorSpace::MatrixID::RGB, ColorSpace::RangeID::FULL);
 
@@ skipping 88 matching lines @@
 
 INSTANTIATE_TEST_CASE_P(
     C,
     ColorSpaceTest,
     testing::Combine(testing::ValuesIn(all_primaries),
                      testing::Values(ColorSpace::TransferID::BT709),
                      testing::ValuesIn(all_matrices),
                      testing::ValuesIn(all_ranges),
                      testing::ValuesIn(intents)));
 }  // namespace