Add 'rxjs' to plugins/package.json

Google-Bug-Id: b/237256547
Release-Notes: skip
Change-Id: I7c419b3d8c2277dba15899adb4cfef218f5aac13
diff --git a/plugins/package.json b/plugins/package.json
index b662e5b..82ebe43 100644
--- a/plugins/package.json
+++ b/plugins/package.json
@@ -6,7 +6,8 @@
     "@gerritcodereview/typescript-api": "3.6.0",
     "@polymer/decorators": "^3.0.0",
     "@polymer/polymer": "^3.4.1",
-    "lit": "^2.2.3"
+    "lit": "^2.2.3",
+    "rxjs": "^6.6.7"
   },
   "license": "Apache-2.0",
   "private": true
diff --git a/plugins/yarn.lock b/plugins/yarn.lock
index f07132d..fa84067 100644
--- a/plugins/yarn.lock
+++ b/plugins/yarn.lock
@@ -59,3 +59,15 @@
     "@lit/reactive-element" "^1.3.0"
     lit-element "^3.2.0"
     lit-html "^2.2.0"
+
+rxjs@^6.6.7:
+  version "6.6.7"
+  resolved "https://registry.yarnpkg.com/rxjs/-/rxjs-6.6.7.tgz#90ac018acabf491bf65044235d5863c4dab804c9"
+  integrity sha512-hTdwr+7yYNIT5n4AMYp85KA6yw2Va0FLa3Rguvbpa4W3I5xynaBZo41cM3XM+4Q6fRMj3sBYIR1VAmZMXYJvRQ==
+  dependencies:
+    tslib "^1.9.0"
+
+tslib@^1.9.0:
+  version "1.14.1"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.14.1.tgz#cf2d38bdc34a134bcaf1091c41f6619e2f672d00"
+  integrity sha512-Xni35NKzjgMrwevysHTCArtLDpPvye8zV/0E4EyYn43P7/7qvQwPh9BGkHewbMulVntbigmcT7rdX3BNo9wRJg==