Remove support for operator negate and replace occurrences with unary

runtime/lib/double.dart

Index: runtime/lib/double.dart
diff --git a/runtime/lib/double.dart b/runtime/lib/double.dart
index c69240c981a2b26b9d91d517e697e2111becdf8c..5c29d8b49732b00eaf2fa26c0f384bdc323f890c 100644
--- a/runtime/lib/double.dart
+++ b/runtime/lib/double.dart
@@ -47,7 +47,7 @@ class Double implements double {
   }
   double remainder_(double other) native "Double_remainder";
 
-  double operator negate() {
+  double operator -() {
     if (this == 0.0) {
       // -0.0 is canonicalized by the VM's parser, therefore no cycles.
       return isNegative() ? 0.0 : -0.0;