Add "Unsafe WebGPU" experimental flag for macOS

This CL promotes the "Unsafe WebGPU" switch to an experimental flag so
that web developers can play easily with the WebGPU API. This flag is
available only on macOS for now.

Bug: 877147
Change-Id: I79273ece367e392f2461c5e51904282f4e764031
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1588385
Reviewed-by: Corentin Wallez <[email protected]>
Commit-Queue: François Beaufort <[email protected]>
Cr-Commit-Position: refs/heads/master@{#655551}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 6866933..186b05f0 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1158,6 +1158,9 @@
 extern const char kUnifiedConsentName[];
 extern const char kUnifiedConsentDescription[];
 
+extern const char kUnsafeWebGPUName[];
+extern const char kUnsafeWebGPUDescription[];
+
 extern const char kUiPartialSwapName[];
 extern const char kUiPartialSwapDescription[];