Roll mojo (flutter/engine#2881)

* Update to mojo ba13534f2b2af27a1d73e176f7406dbab25f8e14

* Fix build for updated mojo

* Fix android build. Undo some of the mojo roll.

* Fix iOS build.

DEPS

@@ -20,7 +20,7 @@
 vars = {
   'chromium_git': 'https://chromium.googlesource.com',
   'fuchsia_git': 'https://fuchsia.googlesource.com',
-  'mojo_sdk_revision': 'b200aa62c93647a0421b9239804ef5ce1509ab20',
+  'mojo_sdk_revision': '6b5fb1227c742f5ecc077486ebc029f2711c61fa',
   'base_revision': '672b04e54b937ec899429a6bd5409c5a6300d151',
   'skia_revision': 'd1bdd1fcbd308afb9903f39d231742f5c951cf07',
 
@@ -286,4 +286,29 @@ hooks = [
         'src/tools',
     ],
   },
+  # Pull the mojom generator binaries using checked-in hashes.
+  {
+    'name': 'mojom_generators',
+    'pattern': '',
+    'action': [ 'download_from_google_storage.py',
+                '--no_resume',
+                '--quiet',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'mojo/mojom_parser/linux64/generators',
+                '-d', 'src/mojo/public/tools/bindings/mojom_tool/bin/linux64/generators',
+    ],
+  },
+  {
+    'name': 'mojom_generators',
+    'pattern': '',
+    'action': [ 'download_from_google_storage.py',
+                '--no_resume',
+                '--quiet',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'mojo/mojom_parser/mac64/generators',
+                '-d', 'src/mojo/public/tools/bindings/mojom_tool/bin/mac64/generators',
+    ],
+  },
 ]

engine/src/flutter/sky/packages/sky_services/pubspec.yaml

@@ -4,6 +4,6 @@ author: Flutter Authors <flutter-dev@googlegroups.com>
 description: Mojom interfaces associated with Flutter
 homepage: http://flutter.io
 dependencies:
-  mojo_sdk: 0.2.29
+  mojo_sdk: 0.2.31
 environment:
   sdk: '>=1.8.0 <2.0.0'