fix some errors in our SDK, mostly around numbers

tool/sdk_expected_errors.txt

Index: tool/sdk_expected_errors.txt
diff --git a/tool/sdk_expected_errors.txt b/tool/sdk_expected_errors.txt
index ace7631e60b631e2e37e50af9c20c703041efd01..dc4c11a0358d0e17e0bdbbab939737ee98556881 100644
--- a/tool/sdk_expected_errors.txt
+++ b/tool/sdk_expected_errors.txt
@@ -1,28 +1,7 @@
 severe: [AnalyzerMessage] Classes cannot implement 'bool' (dart:_interceptors, line 29, col 45)
-severe: [AnalyzerMessage] Classes cannot implement 'num' (dart:_interceptors/js_number.dart, line 16, col 47)
-severe: [AnalyzerMessage] The return type 'JSNumber' is not a 'double', as defined by the method 'toDouble' (dart:_interceptors/js_number.dart, line 110, col 17)
-severe: [StaticTypeError] Type check failed: this (JSNumber) is not of type double (dart:_interceptors/js_number.dart, line 110, col 17)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.& ((num) → num) is not a subtype of int.& ((int) → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.<< ((num) → num) is not a subtype of int.<< ((int) → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.>> ((num) → num) is not a subtype of int.>> ((int) → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.^ ((num) → num) is not a subtype of int.^ ((int) → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of int.abs (() → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of int.sign (() → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of int.unary- (() → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.| ((num) → num) is not a subtype of int.| ((int) → int). (dart:_interceptors/js_number.dart, line 349, col 13)
-severe: [AnalyzerMessage] Classes cannot implement 'int' (dart:_interceptors/js_number.dart, line 349, col 41)
-severe: [AnalyzerMessage] Classes cannot implement 'double' (dart:_interceptors/js_number.dart, line 349, col 46)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.% ((num) → num) is not a subtype of double.% ((num) → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.* ((num) → num) is not a subtype of double.* ((num) → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.+ ((num) → num) is not a subtype of double.+ ((num) → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.- ((num) → num) is not a subtype of double.- ((num) → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of double.abs (() → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.remainder ((num) → num) is not a subtype of double.remainder ((num) → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of double.sign (() → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of double.unary- (() → double). (dart:_interceptors/js_number.dart, line 420, col 16)
-severe: [AnalyzerMessage] Classes cannot implement 'double' (dart:_interceptors/js_number.dart, line 420, col 44)
+severe: [AnalyzerMessage] Classes cannot implement 'int' (dart:_interceptors/js_number.dart, line 12, col 47)
+severe: [AnalyzerMessage] Classes cannot implement 'double' (dart:_interceptors/js_number.dart, line 12, col 52)
 severe: [AnalyzerMessage] Classes cannot implement 'String' (dart:_interceptors/js_string.dart, line 14, col 47)
-severe: [StaticTypeError] Type check failed: s += s (String) is not of type JSString (dart:_interceptors/js_string.dart, line 346, col 7)
 severe: [AnalyzerMessage] The final variable 'lengthInBytes' must be initialized (dart:_native_typed_data, line 24, col 13)
 severe: [AnalyzerMessage] The final variable 'buffer' must be initialized (dart:_native_typed_data, line 427, col 20)
 severe: [AnalyzerMessage] The final variable 'lengthInBytes' must be initialized (dart:_native_typed_data, line 433, col 13)