Implement Double.{toString, toStringAsExponential, toStringAsPrecision}

runtime/lib/double.cc

Index: runtime/lib/double.cc
diff --git a/runtime/lib/double.cc b/runtime/lib/double.cc
index 00c68e823af1033d676c8ada5744f8cd8eaa93b8..5cec30b556a258a1057b2fb21c0c9d20101cda12 100644
--- a/runtime/lib/double.cc
+++ b/runtime/lib/double.cc
@@ -203,12 +203,37 @@ DEFINE_NATIVE_ENTRY(Double_toStringAsFixed, 2) {
 
 
 DEFINE_NATIVE_ENTRY(Double_toStringAsExponential, 2) {
-  UNIMPLEMENTED();
+  const Double& arg = Double::CheckedHandle(arguments->At(0));
+  GET_NATIVE_ARGUMENT(Smi, fraction_digits, arguments->At(1));
+  double d = arg.value();
+  int fraction_digits_value = fraction_digits.Value();
+  String& result = String::Handle();
+  bool succeeded =
+      DoubleToStringAsExponential(d, fraction_digits_value, result);
+  if (!succeeded) {
+    GrowableArray<const Object*> args;
+    args.Add(&String::ZoneHandle(String::New(
+        "Illegal arguments to double.toStringAsExponential")));
+    Exceptions::ThrowByType(Exceptions::kIllegalArgument, args);
+  }
+  arguments->SetReturn(result);
 }
 
 
 DEFINE_NATIVE_ENTRY(Double_toStringAsPrecision, 2) {
-  UNIMPLEMENTED();
+  const Double& arg = Double::CheckedHandle(arguments->At(0));
+  GET_NATIVE_ARGUMENT(Smi, precision, arguments->At(1));
+  double d = arg.value();
+  int precision_value = precision.Value();
+  String& result = String::Handle();
+  bool succeeded = DoubleToStringAsPrecision(d, precision_value, result);
+  if (!succeeded) {
+    GrowableArray<const Object*> args;
+    args.Add(&String::ZoneHandle(String::New(
+        "Illegal arguments to double.toStringAsPrecision")));
+    Exceptions::ThrowByType(Exceptions::kIllegalArgument, args);
+  }
+  arguments->SetReturn(result);
 }