Enable correct optimized double modulo operation. (TODO: enable remainder optimization).

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
===================================================================
--- runtime/vm/code_generator.cc	(revision 17850)
+++ runtime/vm/code_generator.cc	(working copy)
@@ -1717,4 +1717,20 @@
 }
 END_LEAF_RUNTIME_ENTRY
 
+
+double DartModulo(double left, double right) {
+  double remainder = fmod_ieee(left, right);
+  if (remainder == 0.0) {
+    // We explicitely switch to the positive 0.0 (just in case it was negative).
+    remainder = +0.0;
+  } else if (remainder < 0.0) {
+    if (right < 0) {
+      remainder -= right;
+    } else {
+      remainder += right;
+    }
+  }
+  return remainder;
+}
+
 }  // namespace dart