Fix web/_tool/verify_packages

Fix lints in a number of samples

web/slide_puzzle/pubspec.lock

@@ -7,7 +7,7 @@ packages:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.36.0"
+    version: "0.36.4"
   archive:
     dependency: transitive
     description:
@@ -64,6 +64,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.1.2"
+  csslib:
+    dependency: transitive
+    description:
+      name: csslib
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.16.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -80,7 +87,7 @@ packages:
       name: front_end
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.1.15"
+    version: "0.1.19"
   glob:
     dependency: transitive
     description:
@@ -88,6 +95,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.7"
+  html:
+    dependency: transitive
+    description:
+      name: html
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.14.0+2"
   http:
     dependency: transitive
     description:
@@ -101,7 +115,7 @@ packages:
       name: http_multi_server
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.5"
+    version: "2.1.0"
   http_parser:
     dependency: transitive
     description:
@@ -136,14 +150,14 @@ packages:
       name: json_rpc_2
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.10"
+    version: "2.1.0"
   kernel:
     dependency: transitive
     description:
       name: kernel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.15"
+    version: "0.3.19"
   matcher:
     dependency: transitive
     description:
@@ -164,7 +178,7 @@ packages:
       name: mime
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.6+2"
+    version: "0.9.6+3"
   multi_server_socket:
     dependency: transitive
     description:
@@ -178,14 +192,14 @@ packages:
       name: node_preamble
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.4"
+    version: "1.4.8"
   package_config:
     dependency: transitive
     description:
       name: package_config
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0"
   package_resolver:
     dependency: transitive
     description:
@@ -262,7 +276,7 @@ packages:
       name: shelf_web_socket
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.2+5"
+    version: "0.2.3"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -358,21 +372,21 @@ packages:
       name: vm_service_client
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.6+1"
+    version: "0.2.6+3"
   watcher:
     dependency: transitive
     description:
       name: watcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.7+10"
+    version: "0.9.7+12"
   web_socket_channel:
     dependency: transitive
     description:
       name: web_socket_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.12"
+    version: "1.0.15"
   xml:
     dependency: transitive
     description:
@@ -386,6 +400,6 @@ packages:
       name: yaml
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.15"
+    version: "2.1.16"
 sdks:
   dart: ">=2.4.0 <3.0.0"