Update flutter to latest beta branch rev (#564)

diff --git a/Dockerfile b/Dockerfile
index a84fe4c..bba6715 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@
 # To retrieve this value, please run the following in your closest shell:
 #
 # $ (cd flutter && git rev-parse HEAD)
-ARG FLUTTER_COMMIT=f994b769743368b36b9c03fb359f62230b60ab92
+ARG FLUTTER_COMMIT=8fe7655ed20ffd1395f68e30539a847a01a30351
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/cloud_run.Dockerfile b/cloud_run.Dockerfile
index 76c33b6..0a4e0fc 100644
--- a/cloud_run.Dockerfile
+++ b/cloud_run.Dockerfile
@@ -1,12 +1,12 @@
 # Keep aligned with min SDK in pubspec.yaml and Dart test version in .travis.yml
-FROM google/dart:2.8.2
+FROM google/dart:2.8.4
 
 # The specific commit that dart-services should use. This should be kept
 # in sync with the flutter submodule in the dart-services repo.
 # To retrieve this value, please run the following in your closest shell:
 #
 # $ (cd flutter && git rev-parse HEAD)
-ARG FLUTTER_COMMIT=2738a1148ba6c9a6114df62358109407c3ef2553
+ARG FLUTTER_COMMIT=8fe7655ed20ffd1395f68e30539a847a01a30351
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/pubspec.lock b/pubspec.lock
index 97498fe..ca6947f 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -14,7 +14,7 @@
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.0.0"
+    version: "5.0.0"
   analysis_server_lib:
     dependency: "direct main"
     description:
@@ -28,7 +28,7 @@
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.39.10"
+    version: "0.39.12"
   appengine:
     dependency: "direct main"
     description:
@@ -49,14 +49,14 @@
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.4.1"
+    version: "2.4.2"
   bazel_worker:
     dependency: "direct main"
     description:
       name: bazel_worker
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.1.24"
+    version: "0.1.25"
   boolean_selector:
     dependency: transitive
     description:
@@ -91,7 +91,7 @@
       name: build_resolvers
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.9"
+    version: "1.3.10"
   build_runner:
     dependency: "direct dev"
     description:
@@ -147,7 +147,7 @@
       name: code_builder
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.3.0"
+    version: "3.4.0"
   codemirror:
     dependency: "direct dev"
     description:
@@ -161,7 +161,7 @@
       name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.12"
+    version: "1.14.13"
   convert:
     dependency: transitive
     description:
@@ -217,7 +217,7 @@
       name: gcloud
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.2"
+    version: "0.7.3"
   glob:
     dependency: transitive
     description:
@@ -259,7 +259,7 @@
       name: grpc
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.3"
+    version: "2.2.0"
   html:
     dependency: transitive
     description:
@@ -350,14 +350,14 @@
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.6"
+    version: "0.12.8"
   meta:
     dependency: "direct main"
     description:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.8"
+    version: "1.2.2"
   mime:
     dependency: transitive
     description:
@@ -372,13 +372,6 @@
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.0.7"
-  multi_server_socket:
-    dependency: transitive
-    description:
-      name: multi_server_socket
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.0.2"
   node_interop:
     dependency: transitive
     description:
@@ -420,7 +413,7 @@
       name: pedantic
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.0"
+    version: "1.9.2"
   pool:
     dependency: transitive
     description:
@@ -462,7 +455,7 @@
       name: shelf
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.5"
+    version: "0.7.7"
   shelf_packages_handler:
     dependency: transitive
     description:
@@ -504,7 +497,7 @@
       name: source_gen
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.5"
+    version: "0.9.6"
   source_map_stack_trace:
     dependency: transitive
     description:
@@ -532,7 +525,7 @@
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "1.9.5"
   stream_channel:
     dependency: transitive
     description:
@@ -560,7 +553,7 @@
       name: synchronized
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.2.0"
+    version: "2.2.0+1"
   term_glyph:
     dependency: transitive
     description:
@@ -574,21 +567,21 @@
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.7"
+    version: "1.15.2"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.16"
+    version: "0.2.17"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.7"
+    version: "0.3.10"
   timing:
     dependency: transitive
     description:
@@ -609,14 +602,14 @@
       name: typed_data
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.6"
+    version: "1.2.0"
   uuid:
     dependency: "direct main"
     description:
       name: uuid
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.4"
+    version: "2.2.0"
   vm_service:
     dependency: transitive
     description: