Use the Dart SDK built from Flutter engine rather than from dartlang.org (#14610)

* Use engine-built dart sdk

* Download dart-sdk from engine

* Move up deps to fix dart sdk constraint problem

* Update update_dart_sdk.ps1 for Windows

* Fix tests so they pass analysis

* More types for tests

* Roll engine

* Update dart sdk stamp location in flutter.bat

* Add newline
diff --git a/examples/flutter_gallery/pubspec.yaml b/examples/flutter_gallery/pubspec.yaml
index e3b8174..de45c37 100644
--- a/examples/flutter_gallery/pubspec.yaml
+++ b/examples/flutter_gallery/pubspec.yaml
@@ -24,7 +24,7 @@
     sdk: flutter
 
   args: 1.3.0 # TRANSITIVE DEPENDENCY
-  async: 2.0.3 # TRANSITIVE DEPENDENCY
+  async: 2.0.4 # TRANSITIVE DEPENDENCY
   barback: 0.15.2+14 # TRANSITIVE DEPENDENCY
   boolean_selector: 1.0.2 # TRANSITIVE DEPENDENCY
   charcode: 1.1.1 # TRANSITIVE DEPENDENCY
@@ -32,7 +32,7 @@
   convert: 2.0.1 # TRANSITIVE DEPENDENCY
   crypto: 2.0.2+1 # TRANSITIVE DEPENDENCY
   csslib: 0.14.1 # TRANSITIVE DEPENDENCY
-  file: 2.3.5 # TRANSITIVE DEPENDENCY
+  file: 2.3.6 # TRANSITIVE DEPENDENCY
   glob: 1.1.5 # TRANSITIVE DEPENDENCY
   html: 0.13.2+2 # TRANSITIVE DEPENDENCY
   http: 0.11.3+16 # TRANSITIVE DEPENDENCY
@@ -44,9 +44,9 @@
   json_rpc_2: 2.0.7 # TRANSITIVE DEPENDENCY
   logging: 0.11.3+1 # TRANSITIVE DEPENDENCY
   matcher: 0.12.1+4 # TRANSITIVE DEPENDENCY
-  meta: 1.1.1 # TRANSITIVE DEPENDENCY
+  meta: 1.1.2 # TRANSITIVE DEPENDENCY
   mime: 0.9.6 # TRANSITIVE DEPENDENCY
-  mockito: 2.2.2 # TRANSITIVE DEPENDENCY
+  mockito: 2.2.3 # TRANSITIVE DEPENDENCY
   multi_server_socket: 1.0.1 # TRANSITIVE DEPENDENCY
   node_preamble: 1.4.0 # TRANSITIVE DEPENDENCY
   package_config: 1.0.3 # TRANSITIVE DEPENDENCY
@@ -66,13 +66,13 @@
   stack_trace: 1.9.1 # TRANSITIVE DEPENDENCY
   stream_channel: 1.6.3 # TRANSITIVE DEPENDENCY
   term_glyph: 1.0.0 # TRANSITIVE DEPENDENCY
-  test: 0.12.30+2 # TRANSITIVE DEPENDENCY
-  typed_data: 1.1.4 # TRANSITIVE DEPENDENCY
+  test: 0.12.30+3 # TRANSITIVE DEPENDENCY
+  typed_data: 1.1.5 # TRANSITIVE DEPENDENCY
   utf: 0.9.0+4 # TRANSITIVE DEPENDENCY
   vector_math: 2.0.5 # TRANSITIVE DEPENDENCY
   vm_service_client: 0.2.4+1 # TRANSITIVE DEPENDENCY
   watcher: 0.9.7+7 # TRANSITIVE DEPENDENCY
-  web_socket_channel: 1.0.6 # TRANSITIVE DEPENDENCY
+  web_socket_channel: 1.0.7 # TRANSITIVE DEPENDENCY
   yaml: 2.1.13 # TRANSITIVE DEPENDENCY
 
 flutter: