Add Vulkan validation layers on Windows

Deploy self-built Vulkan validation layers instead of system installed
one. And it will reuse third_party/angle's Vulkan validation layers if
building with chromium.

Bug: dawn:150
Change-Id: I94e26f7a152fb2a1c39bcb102d60024f4d65eee6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/11120
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/tests/unittests/SystemUtilsTests.cpp

@@ -0,0 +1,41 @@
+// Copyright 2019 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <gtest/gtest.h>
+
+#include "common/SystemUtils.h"
+
+// Tests for GetEnvironmentVar
+TEST(SystemUtilsTests, GetEnvironmentVar) {
+    // Test nonexistent environment variable
+    ASSERT_EQ(GetEnvironmentVar("NonexistentEnvironmentVar"), "");
+}
+
+// Tests for SetEnvironmentVar
+TEST(SystemUtilsTests, SetEnvironmentVar) {
+    // Test new environment variable
+    ASSERT_TRUE(SetEnvironmentVar("EnvironmentVarForTest", "NewEnvironmentVarValue"));
+    ASSERT_EQ(GetEnvironmentVar("EnvironmentVarForTest"), "NewEnvironmentVarValue");
+    // Test override environment variable
+    ASSERT_TRUE(SetEnvironmentVar("EnvironmentVarForTest", "OverrideEnvironmentVarValue"));
+    ASSERT_EQ(GetEnvironmentVar("EnvironmentVarForTest"), "OverrideEnvironmentVarValue");
+}
+
+// Tests for GetExecutableDirectory
+TEST(SystemUtilsTests, GetExecutableDirectory) {
+    // Test returned value is non-empty string
+    ASSERT_NE(GetExecutableDirectory(), "");
+    // Test last charecter in path
+    ASSERT_EQ(GetExecutableDirectory().back(), *GetPathSeparator());
+}