Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /cc

This CL was uploaded by git cl split.

R=majidvp@chromium.org

Bug: 1110266
Change-Id: Icbd028234d6de8b2ef5b2e4dd52b8107006eea86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371213Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#801802}

cc/test/layer_tree_test.cc

@@ -666,7 +666,7 @@ LayerTreeTest::LayerTreeTest(TestRendererType renderer_type)
     init_vulkan = true;
   } else if (renderer_type_ == TestRendererType::kSkiaDawn) {
     scoped_feature_list_.InitAndEnableFeature(features::kSkiaDawn);
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
     init_vulkan = true;
 #elif defined(OS_WIN)
     // TODO(sgilhuly): Initialize D3D12 for Windows.

cc/test/pixel_test.cc

@@ -69,7 +69,7 @@ PixelTest::PixelTest(GraphicsBackend backend)
     init_vulkan = true;
   } else if (backend == kSkiaDawn) {
     scoped_feature_list_.InitAndEnableFeature(features::kSkiaDawn);
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
     init_vulkan = true;
 #elif defined(OS_WIN)
     // TODO(sgilhuly): Initialize D3D12 for Windows.

cc/trees/layer_tree_host_pixeltest_tiles.cc

@@ -210,7 +210,7 @@ INSTANTIATE_TEST_SUITE_P(All,
                          LayerTreeHostTilesTestPartialInvalidationMultiThread,
                          ::testing::ValuesIn(kTestCasesMultiThread));
 
-#if defined(OS_LINUX) && defined(THREAD_SANITIZER)
+#if (defined(OS_LINUX) || defined(OS_CHROMEOS)) && defined(THREAD_SANITIZER)
 // Flaky on Linux TSAN. https://crbug.com/707711
 #define MAYBE_PartialRaster DISABLED_PartialRaster
 #elif defined(OS_WIN) && defined(ADDRESS_SANITIZER)