[infra] Add ninja to the SDK DEPS

This will allow us to gradually migrate from depot_tools ninja to our
own. See also https://crbug.com/1340825.

Bug: https://github.com/dart-lang/sdk/issues/50032
Change-Id: I5118c98abcb4399ec5d952c5a3e240f8e3803475
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/260762
Reviewed-by: William Hesse <whesse@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

DEPS

@@ -69,6 +69,9 @@ vars = {
   "clang_revision": "c2592c374e469f343ecea82d6728609650924259",
   "gn_revision": "d7c2209cebcfe37f46dba7be4e1a7000ffc342fb",
 
+  # Ninja, runs the build based on files generated by GN.
+  "ninja_tag": "version:2@1.11.1.chromium.4",
+
   # Scripts that make 'git cl format' work.
   "clang_format_scripts_rev": "bb994c6f067340c1135eb43eed84f4b33cfa7397",
 
@@ -509,6 +512,14 @@ deps = {
       "dep_type": "cipd",
   },
 
+  Var("dart_root") + "/buildtools/ninja": {
+      "packages": [{
+          "package": "infra/3pp/tools/ninja/${{platform}}",
+          "version": Var("ninja_tag"),
+      }],
+      "dep_type": "cipd",
+  },
+
   Var("dart_root") + "/third_party/android_tools/ndk": {
       "packages": [
           {