Update documentation on trignometric functions.

pkg/analysis_server/test/mock_sdk.dart

Index: pkg/analysis_server/test/mock_sdk.dart
diff --git a/pkg/analysis_server/test/mock_sdk.dart b/pkg/analysis_server/test/mock_sdk.dart
index 82b6b79f899d5c651b06b13b29dfb6f84c4b05a2..0697130f88335a82b092887bc0d43768aa8f942b 100644
--- a/pkg/analysis_server/test/mock_sdk.dart
+++ b/pkg/analysis_server/test/mock_sdk.dart
@@ -225,9 +225,9 @@ 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 cos(num radians);
 external num pow(num x, num exponent);
-external double sin(num x);
+external double sin(num radians);
 external double sqrt(num x);
 class Random {
   bool nextBool() => true;