[sdk] Update checked-in SDKs to 2.13.1

* This adds a mac amd64 SDK as the arm64 SDK to bootstrap arm64
  development on macOS.

Change-Id: I519e5ad2343360bc2e692b52d95c94076bfd9e87
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/201833
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
diff --git a/DEPS b/DEPS
index cf9edd4..ba07759 100644
--- a/DEPS
+++ b/DEPS
@@ -39,7 +39,7 @@
 
   # Checked-in SDK version. The checked-in SDK is a Dart SDK distribution in a
   # cipd package used to run Dart scripts in the build and test infrastructure.
-  "sdk_tag": "version:2.13.0-211.14.beta",
+  "sdk_tag": "version:2.13.1",
 
   # co19 is a cipd package. Use update.sh in tests/co19[_2] to update these
   # hashes. It requires access to the dart-build-access group, which EngProd
diff --git a/tools/sdks/update.sh b/tools/sdks/update.sh
index df63b09..1d33b82 100755
--- a/tools/sdks/update.sh
+++ b/tools/sdks/update.sh
@@ -61,6 +61,17 @@
   -ref $channel
 rm -rf sdk
 
+# TODO(athom): Use a proper arm64 SDK when available.
+gsutil.py cp "gs://dart-archive/channels/$channel/release/$1/sdk/dartsdk-macos-x64-release.zip" .
+unzip -q dartsdk-macos-x64-release.zip -d sdk
+cipd create \
+  -name dart/dart-sdk/mac-arm64 \
+  -in sdk \
+  -install-mode copy \
+  -tag version:$1 \
+  -ref $channel
+rm -rf sdk
+
 gsutil.py cp "gs://dart-archive/channels/$channel/release/$1/sdk/dartsdk-windows-x64-release.zip" .
 unzip -q dartsdk-windows-x64-release.zip -d sdk
 cipd create \