Update documentation on trignometric functions.

pkg/analyzer/test/src/context/mock_sdk.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.src.context.mock_sdk;
 
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
@@ skipping 365 matching lines @@
     '''
 library dart.math;
 
 const double E = 2.718281828459045;
 const double PI = 3.1415926535897932;
 const double LN10 =  2.302585092994046;
 
 T min<T extends num>(T a, T b) => null;
 T max<T extends num>(T a, T b) => null;
 
-external double cos(num x);
-external double sin(num x);
-external double sqrt(num x);
+external double cos(num radians);
+external double sin(num radians);
+external double sqrt(num radians);
 class Random {
   bool nextBool() => true;
   double nextDouble() => 2.0;
   int nextInt() => 1;
 }
 ''');
 
 const List<SdkLibrary> _LIBRARIES = const [
   _LIB_CORE,
   _LIB_ASYNC,
@@ skipping 225 matching lines @@
 
   @override
   AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
     if (factory == null) {
       return super.createCacheFromSourceFactory(factory);
     }
     return new AnalysisCache(
         <CachePartition>[AnalysisEngine.instance.partitionManager.forSdk(sdk)]);
   }
 }