Add WebGPUCompatibilityMode origin trial tokens

[beaufortfrancois]

This PR adds tokens for the WebGPU compatibility mode origin trial:

• one for https://webgpu.github.io (production URL) expiring April 21, 2026
• one for http://localhost:8080 (development URL) expiring April 21, 2026

[beaufortfrancois]

FYI @SenorBlanco

[SenorBlanco]

Thanks for doing this!

one for http://localhost:8080/

Good idea! I didn't even know that worked.

[SenorBlanco]

This doesn't seem to be working. Compatibiilty mode still seems to require enabling "WebGPU Developer Features" in chrome://flags.

[beaufortfrancois]

According to DevTools, the WebCompatibiiltyMode OT token is working. See the Chrome Canary screenshot below:

Note that it is not working in Chrome Stable though as the trial starts in Chrome 139. See:

[beaufortfrancois]

Note that I'm surprised "WebGPU Developer Features" is required for WebGPU compatibility mode as my understanding it had nothing to do with it. Did you mean "WebGPU Experimental Features"?

[SenorBlanco]

Sorry, I should've been more clear. I tried it on Canary in three older Android devices which should be working after my blocklist change last week:

Lenovo Tab M8 Gen4 (PowerVR Rogue GE8300)
Redmi A5 (PowerVR Rogue GE8320)
Samsung Tab S4 (Qualcomm Adreno 540)

and they all failed as above.
chrome://gpu shows WebGPU: Hardware Accelerated, and the Dawn Info shows the OpenGLES driver with [WebGPU Status] Available.

It actually does start working with "WebGPU Developer Features" enabled (this was a mistake, I meant to enable Experimental features), but this is an interesting datapoint. I can't figure out what "Developer Features" is enabling that would cause Compat mode to work.

[SenorBlanco]

(Note that "WebGPU Developer Features" is exposed in chrome://flags, while "WebGPU Experimental Features" is not. So the former is easy to enable in Canary while the latter requires command-line flags.)

[SenorBlanco]

Another datapoint: on a local build of Chrome/Linux (GL), these flags cause the samples to work:
out/Release/chrome --enable-features=WebGPUService,WebGPUCompatibilityMode

This doesn't:
out/Release/chrome --enable-features=WebGPUService

[SenorBlanco]

This looks like a Chrome bug; filed here: https://issues.chromium.org/issues/430248354. Sorry for the noise.

[beaufortfrancois]

Oh! According to the code below, "WebGPU Developer Features" is actually enabling WebGPU Compatibility Mode.

  if (force_webgpu_compat_ ||
      (static_cast<wgpu::FeatureLevel>(options->featureLevel) ==
           wgpu::FeatureLevel::Compatibility &&
       (safety_level_ == webgpu::SafetyLevel::kUnsafe ||
        safety_level_ == webgpu::SafetyLevel::kSafeExperimental || // <-- this is true with WebGPU Developer Features
        base::FeatureList::IsEnabled(features::kWebGPUCompatibilityMode)))) {
    feature_level = wgpu::FeatureLevel::Compatibility;
  }

Source: https://source.chromium.org/chromium/chromium/src/+/main:gpu/command_buffer/service/webgpu_decoder_impl.cc;l=1349;drc=b97f6486e3ccf883f2e2f085abfb4829d8ca6f8d

  if (gpu_preferences.enable_webgpu_developer_features ||
      gpu_preferences.enable_webgpu_experimental_features) {
    safety_level_ = webgpu::SafetyLevel::kSafeExperimental;
  }

Source: https://source.chromium.org/chromium/chromium/src/+/main:gpu/command_buffer/service/webgpu_decoder_impl.cc;l=1132;drc=b97f6486e3ccf883f2e2f085abfb4829d8ca6f8d

Moreover, "WebGPU Experimental Features" is a experimental blink runtime feature. It means users can enable it by enabling the "Experimental Web Platform Features" flag in chrome://flags

    {
      // WebGPU experimental features are meant for features that would
      // eventually land in the WebGPU spec.
      name: "WebGPUExperimentalFeatures",
      status: "experimental",
      public: true,
    },
    ```