Default dawn_use_swiftshader to true

SwiftShader is required to implement WebGPU fallback adapters.

Perf tests are skipped for CPU adapters since they easily timeout
for intensive benchmarks.

Bug: chromium:1266550
Change-Id: Ib6e91da1128baae1770c797a69cf9ad605ea324d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/76421
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>

scripts/dawn_features.gni

@@ -32,13 +32,9 @@ dawn_is_winuwp = is_win && target_os == "winuwp"
 declare_args() {
   dawn_use_angle = true
 
-  # Enables usage of swiftshader on the Vulkan backend.
-  # Note that this will only work in standalone and in projects that set the
-  # dawn_swiftshader_dir variable in build_overrides/dawn.gni
-  # Because of how the Vulkan loader works, setting this makes Dawn only able
-  # to find the Swiftshader ICD and not the others.
-  # Enabled by default when fuzzing.
-  dawn_use_swiftshader = build_with_chromium && use_fuzzing_engine
+  # Enables SwiftShader as the fallback adapter. Requires dawn_swiftshader_dir
+  # to be set to take effect.
+  dawn_use_swiftshader = true
 }
 
 declare_args() {

src/tests/perf_tests/DawnPerfTest.h

@@ -115,6 +115,13 @@ class DawnPerfTestWithParams : public DawnTestWithParams<Params>, public DawnPer
         : DawnTestWithParams<Params>(),
           DawnPerfTestBase(this, iterationsPerStep, maxStepsInFlight) {
     }
+    void SetUp() override {
+        DawnTestWithParams<Params>::SetUp();
+
+        wgpu::AdapterProperties properties;
+        this->GetAdapter().GetProperties(&properties);
+        DAWN_TEST_UNSUPPORTED_IF(properties.adapterType == wgpu::AdapterType::CPU);
+    }
     ~DawnPerfTestWithParams() override = default;
 };