Roll Dart to 635c47b. (flutter#13315)

635c47b Reland "Update BoringSSL to 4dfd5af."
2be3763 [vm/ffi] Support moves with temp in ffi call
92c69f2 Flow analysis: promote on successful execution of an "as" expression.
6461e41 Flow analysis: call initialize for params after functionExpression_begin.
5837c65 Flow analysis: test unreachability for constructor initializers.
8e23f76 Flow analysis: properly handle promotion of type parameters.
a7b092e Fix operator== for type parameter types.
06a8577 Flow analysis: recursively annotate unreachable nodes in test

DEPS

@@ -34,16 +34,16 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': 'b359ac0a1e5b2fa16ec71d6e5788f53b82903057',
+  'dart_revision': '635c47b1c9efe86b896d95bd446c6a5e2459037e',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
   'dart_args_tag': '1.5.2',
   'dart_async_tag': '2.0.8',
   'dart_bazel_worker_tag': 'bazel_worker-v0.1.20',
   'dart_boolean_selector_tag': '1.0.4',
-  'dart_boringssl_gen_rev': 'bbf52f18f425e29b1185f2f6753bec02ed8c5880',
-  'dart_boringssl_rev': '702e2b6d3831486535e958f262a05c75a5cb312e',
+  'dart_boringssl_gen_rev': 'b9e27cff1ff0803e97ab1f88764a83be4aa94a6d',
+  'dart_boringssl_rev': '4dfd5af70191b068aebe567b8e29ce108cee85ce',
   'dart_charcode_tag': 'v1.1.2',
   'dart_cli_util_rev': '4ad7ccbe3195fd2583b30f86a86697ef61e80f41',
   'dart_collection_tag': '1.14.11',