Enable Vulkan validation layers on Linux

When vkDestroyDebugReportCallbackEXT() is called in Backend::~Backend()
and Vulkan validation layers are in use, the variable unique_id_mapping
is referenced internally[1]. However, the variable is global[2] and it's
destructed before Backend::~Backend(), which causes a use-after-free
issue. The issue was unnoticed on Windows, but we observed the crash at
exit on Linux.

[1] 9fba37afae/layers/generated/layer_chassis_dispatch.cpp (4961)
[2] 9fba37afae/layers/generated/chassis.cpp (40)

Bug: dawn:150
Change-Id: I505373a88ef9795243dd18da9785fb49d253e498
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/13787
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

scripts/dawn_features.gni

@@ -49,7 +49,9 @@ declare_args() {
 # GN does not allow reading a variable defined in the same declare_args().
 # Put them in two separate declare_args() when setting the value of one
 # argument based on another.
-declare_args() {
+if (dawn_enable_vulkan) {
+  declare_args() {
     # Uses our built version of Vulkan validation layers
-  dawn_enable_vulkan_validation_layers = dawn_enable_vulkan && is_win
+    dawn_enable_vulkan_validation_layers = is_linux || is_win
+  }
 }

src/tests/DawnTest.cpp

@@ -214,6 +214,12 @@ void DawnTestEnvironment::SetUp() {
     std::cout << std::endl;
 }
 
+void DawnTestEnvironment::TearDown() {
+    // When Vulkan validation layers are enabled, it's unsafe to call Vulkan APIs in the destructor
+    // of a static/global variable, so the instance must be manually released beforehand.
+    mInstance.reset();
+}
+
 bool DawnTestEnvironment::UsesWire() const {
     return mUseWire;
 }

src/tests/DawnTest.h

@@ -130,6 +130,7 @@ class DawnTestEnvironment : public testing::Environment {
     static void SetEnvironment(DawnTestEnvironment* env);
 
     void SetUp() override;
+    void TearDown() override;
 
     bool UsesWire() const;
     bool IsBackendValidationEnabled() const;