[infra] Introduce devtools_rev in DEPS

That way we can pick it up in the Flutter roller in
`src/tools/dart/create_updated_flutter_deps.py`.

Change-Id: I2b64e5790de3737dc0d66069aecdd99b42b7c2c9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/198042
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
diff --git a/DEPS b/DEPS
index e68ae1c..1124ea3 100644
--- a/DEPS
+++ b/DEPS
@@ -107,6 +107,7 @@
 
   "chromedriver_tag": "83.0.4103.39",
   "dartdoc_rev" : "505f163f7cb48e917503e4a23fbff1227e08b263",
+  "devtools_rev" : "12ad5341ae0a275042c84a4e7be9a6c98db65612",
   "jsshell_tag": "version:88.0",
   "ffi_rev": "f3346299c55669cc0db48afae85b8110088bf8da",
   "fixnum_rev": "16d3890c6dc82ca629659da1934e412292508bba",
@@ -246,7 +247,7 @@
   Var("dart_root") + "/third_party/devtools": {
       "packages": [{
           "package": "dart/third_party/flutter/devtools",
-          "version": "git_revision:12ad5341ae0a275042c84a4e7be9a6c98db65612",
+          "version": "git_revision:" + Var("devtools_rev"),
       }],
       "dep_type": "cipd",
   },