Add pubspec.yaml to runtime/tools

Otherwise Dart scripts there inherit the version from the root
pubspec, which can be ahead of prebuilt SDK.

Change-Id: I07b6672f72c08d73661fda4e333cbc2be767db52
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/440480
Reviewed-by: Alexander Thomas <athom@google.com>
Auto-Submit: Ivan Inozemtsev <iinozemtsev@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>

https://dart.googlesource.com/sdk/+/27c2cfb3f7a4c7e548b10aa338cc2b38bccbad36

DEPS

diff --git a/DEPS b/DEPS
index ded2650..b699306 100644
--- a/DEPS
+++ b/DEPS
@@ -229,7 +229,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'bf2870c52b1cc03e2ec682ea5d01d372680da775',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '27c2cfb3f7a4c7e548b10aa338cc2b38bccbad36',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '6e1ebc7a13b8fe72d796f8335876b3e44dc68450',
 

commits.json

diff --git a/commits.json b/commits.json
index 6c6c45b..fc46c66 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"6e1ebc7a13b8fe72d796f8335876b3e44dc68450",
-  "flutter/engine/src/flutter/third_party/dart":"bf2870c52b1cc03e2ec682ea5d01d372680da775"
+  "flutter/engine/src/flutter/third_party/dart":"27c2cfb3f7a4c7e548b10aa338cc2b38bccbad36"
 }
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