Query API: Test the accuracy of timestamp compute shader

Because the uint64 is not supported on all GPU drivers, we use uint32
and float to simulate the multiplication of uint64, but there is
accuracy loss between the results and the expected results computed by
uint64. This test checks that the accuracy loss is less than 0.2%.

Bug: dawn:434
Change-Id: I6f5c842b6915f101441886bdfa4f9feb2827d174
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/34120
Commit-Queue: Hao Li <hao.x.li@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/InternalPipelineStore.h

@@ -28,6 +28,9 @@ namespace dawn_native {
         Ref<RenderPipelineBase> copyTextureForBrowserPipeline;
         Ref<ShaderModuleBase> copyTextureForBrowserVS;
         Ref<ShaderModuleBase> copyTextureForBrowserFS;
+
+        Ref<ComputePipelineBase> timestampComputePipeline;
+        Ref<ShaderModuleBase> timestampCS;
     };
 }  // namespace dawn_native