Revert "[msl] Remove PixelLocal as printer supported extension"

This reverts commit e5f014098bf1706bbf04f5a507ee8b8d04cbfba5.

Reason for revert: Causes failures when the pixel local extension is enabled, but no pixel local variables are used.

Original change's description:
> [msl] Remove PixelLocal as printer supported extension
>
> At this point in the pipeline, it should have been transformed into a framebuffer-fetch.
>
> Bug: tint:2085
> Change-Id: If3da836395ffd755c2ef1d677cf096714b7ec10b
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/160840
> Auto-Submit: Ben Clayton <bclayton@google.com>
> Kokoro: Kokoro <noreply+kokoro@google.com>
> Reviewed-by: dan sinclair <dsinclair@chromium.org>
> Commit-Queue: dan sinclair <dsinclair@chromium.org>

TBR=dsinclair@chromium.org,bclayton@google.com,jrprice@google.com,noreply+kokoro@google.com,dawn-scoped@luci-project-accounts.iam.gserviceaccount.com

Change-Id: I884cb051a87f4e32e458b720bd64156a8da6ae95
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: tint:2085
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/161016
Kokoro: Ben Clayton <bclayton@google.com>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/lang/msl/writer/ast_printer/ast_printer.cc b/src/tint/lang/msl/writer/ast_printer/ast_printer.cc
index a02c250..60f7f81 100644
--- a/src/tint/lang/msl/writer/ast_printer/ast_printer.cc
+++ b/src/tint/lang/msl/writer/ast_printer/ast_printer.cc
@@ -274,11 +274,10 @@
     if (!tint::wgsl::CheckSupportedExtensions(
             "MSL", builder_.AST(), diagnostics_,
             Vector{
-                // Note: kChromiumExperimentalPixelLocal should have been transformed into
-                // kChromiumExperimentalFramebufferFetch by the PixelLocal transform.
                 wgsl::Extension::kChromiumDisableUniformityAnalysis,
                 wgsl::Extension::kChromiumExperimentalDp4A,
                 wgsl::Extension::kChromiumExperimentalFullPtrParameters,
+                wgsl::Extension::kChromiumExperimentalPixelLocal,
                 wgsl::Extension::kChromiumExperimentalReadWriteStorageTexture,
                 wgsl::Extension::kChromiumExperimentalSubgroups,
                 wgsl::Extension::kChromiumExperimentalFramebufferFetch,