Fix the beta build

[kwalrath]

The beta and dev builds are failing. That's OK for dev... but shouldn't be OK for beta. Because this has been failing since the very first 2.9 beta, I'm guessing 2.9 is just pickier than 2.8. Some of these errors we might be able to ignore using comments like // ignore_for_file: some_analyzer_error_or_warning_id.

Example: https://travis-ci.org/github/dart-lang/site-www/jobs/708518273

The problems are under examples/misc & :

PROCESSING /home/travis/build/dart-lang/site-www/examples/misc
...
  error • A value of type 'dynamic' can't be assigned to a variable of type 'int'. • bin/try_dart/functions.dart:12:9 • invalid_assignment
  error • A value of type 'num' can't be assigned to a variable of type 'int'. • lib/effective_dart/design_bad.dart:79:38 • invalid_assignment
  error • All final variables must be initialized, but 'contents' isn't. • lib/effective_dart/usage_bad.dart:370:3 • final_not_initialized_constructor
  error • The argument type 'int' can't be assigned to the parameter type 'String'. • lib/language_tour/generics/misc.dart:9:15 • argument_type_not_assignable
  error • 'Object' doesn't extend 'SomeBaseClass'. • lib/language_tour/generics/misc.dart:29:19 • type_argument_not_matching_bounds
  error • The argument type 'int' can't be assigned to the parameter type 'String'. • lib/library_tour/core/collections.dart:5:14 • argument_type_not_assignable
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Person'. • lib/library_tour/core/hash_code.dart:24:21 • invalid_assignment
7 errors found.
...
PROCESSING /home/travis/build/dart-lang/site-www/examples/strong
...
  error • 'HoneyBadger.parent' ('Root Function()') isn't a valid override of 'Animal.parent' ('Animal Function()'). • lib/animal_bad.dart:15:12 • invalid_override
  error • 'Cat.chase' ('void Function(Mouse)') isn't a valid override of 'Animal.chase' ('void Function(Animal)'). • lib/animal_bad.dart:26:8 • invalid_override
  error • A value of type 'List<dynamic>' can't be assigned to a variable of type 'List<Cat>'. • lib/animal_bad.dart:48:19 • invalid_assignment
  error • The method 'add' isn't defined for the type 'Iterable'. • lib/bounded/instantiate_to_bound.dart:7:5 • undefined_method
  error • A value of type 'Element' can't be assigned to a variable of type 'CanvasElement'. • lib/common_fixes_analysis.dart:21:28 • invalid_assignment
  error • A value of type 'int' can't be assigned to a variable of type 'bool'. • lib/common_problems_analysis.dart:14:14 • invalid_assignment
  error • The getter 'context2D' isn't defined for the type 'Element'. • lib/common_problems_analysis.dart:23:12 • undefined_getter
  error • A value of type 'double' can't be assigned to a variable of type 'int'. • lib/common_problems_analysis.dart:38:16 • invalid_assignment
  error • A value of type 'List<int>' can't be assigned to a variable of type 'List<String>'. • lib/common_problems_analysis.dart:46:27 • invalid_assignment
  error • 'MyAdder.add' ('int Function(int, int)') isn't a valid override of 'NumberAdder.add' ('num Function(num, num)'). • lib/common_problems_analysis.dart:61:7 • invalid_override
  error • 'Subclass.method' ('void Function(int)') isn't a valid override of 'Superclass.method' ('void Function(dynamic)'). • lib/common_problems_analysis.dart:74:8 • invalid_override
  error • The super call must be last in an initializer list (see https://goo.gl/EY6hDP): 'super(food)'. • lib/common_problems_analysis.dart:92:9 • invalid_super_invocation
  error • The function expression type 'bool Function(String)' isn't of type 'bool Function(dynamic)'. This means its parameter or return type doesn't match what is expected. Consider changing parameter type(s) or the returned type(s). • lib/common_problems_analysis.dart:102:17 • invalid_cast_function_expr
  error • A value of type 'bool Function(String)' can't be assigned to a variable of type 'bool Function(dynamic)'. • lib/common_problems_analysis.dart:102:17 • invalid_assignment
  error • The class 'MyList' cannot implement both 'List<int*>*' and 'List<dynamic>*' because the type arguments are different. • lib/dart_1_my_list_hello_world.dart:11:1 • conflicting_generic_interfaces
  error • Superinterfaces don't have a valid override for '+': ListMixin.+ (List<int> Function(List<int>)), List.+ (List<dynamic> Function(List<dynamic>)). • lib/dart_1_my_list_hello_world.dart:11:7 • inconsistent_inheritance
  error • 'ListMixin.add' ('void Function(int)') isn't a valid override of 'List.add' ('void Function(dynamic)'). • lib/dart_1_my_list_hello_world.dart:11:7 • invalid_override
  error • 'MyList.length' ('Object Function()') isn't a valid override of 'List.length' ('int Function()'). • lib/dart_1_my_list_hello_world.dart:12:10 • invalid_override
  error • A value of type 'String' can't be returned from method '[]' because it has a return type of 'int'. • lib/dart_1_my_list_hello_world.dart:16:25 • return_of_invalid_type
  error • The argument type 'List<dynamic>' can't be assigned to the parameter type 'List<int>'. • lib/strong_analysis.dart:27:17 • argument_type_not_assignable
  error • The argument type 'int' can't be assigned to the parameter type 'String'. • lib/strong_analysis.dart:38:15 • argument_type_not_assignable
  error • The argument type 'int' can't be assigned to the parameter type 'String'. • lib/strong_analysis.dart:54:15 • argument_type_not_assignable
  error • A value of type 'double' can't be assigned to a variable of type 'int'. • lib/strong_analysis.dart:82:9 • invalid_assignment
  error • A value of type 'String' can't be assigned to a variable of type 'double'. • lib/strong_analysis.dart:106:23 • invalid_assignment
  error • A value of type 'Cat' can't be assigned to a variable of type 'MaineCoon'. • lib/strong_analysis.dart:118:19 • invalid_assignment
  error • A value of type 'List<Animal>' can't be assigned to a variable of type 'List<Cat>'. • lib/strong_analysis.dart:144:24 • invalid_assignment
  error • A value of type 'int' can't be assigned to a variable of type 'String'. • lib/strong_analysis.dart:157:21 • invalid_assignment
  error • A value of type 'List<dynamic>' can't be assigned to a variable of type 'List<int>'. • test/strong_test.dart:42:27 • invalid_assignment
  error • A value of type 'List<Animal>' can't be assigned to a variable of type 'List<Cat>'. • test/strong_test.dart:64:26 • invalid_assignment
  error • A value of type 'List<Object>' can't be assigned to a variable of type 'List<String>'. • test/strong_test.dart:178:26 • invalid_assignment
30 errors found.
No analysis errors or warnings should be present in original source files.
Ensure that these issues are disabled using appropriate markers like: 
  // ignore_for_file: beta, some_analyzer_error_or_warning_id

[kwalrath]

Thea and I fixed this in #2575! But then it broke again. :(

https://travis-ci.org/github/dart-lang/site-www/jobs/719352447