Add Adapter::SupportsExternalImages

This commit adds a getter so that Chromium can check whether an
Adapter would support external images. External images are
necessary to implement the WebGPU swapchain and interop with the
rest of the web platform. We should not expose adapters that
cannot interop with the canvas and other web platform primitives
until WebGPU gains options to request more "limited" adapters.

Bug: dawn:1056
Change-Id: Iff83ac26b0e92dccdd4e29c0d854d9276a4a37bc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/61580
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Brian Ho <hob@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/include/dawn_native/DawnNative.h

@@ -109,6 +109,10 @@ namespace dawn_native {
         std::vector<const char*> GetSupportedExtensions() const;
         WGPUDeviceProperties GetAdapterProperties() const;
 
+        // Check that the Adapter is able to support importing external images. This is necessary
+        // to implement the swapchain and interop APIs in Chromium.
+        bool SupportsExternalImages() const;
+
         explicit operator bool() const;
 
         // Create a device on this adapter, note that the interface will change to include at least