Harmony: implement Math.sign.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index c48385ce11ccec616e5435ee198b8b0d55ba23a6..234a2118bdd7002189906df3e21f6446869f594e 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -2067,6 +2067,11 @@ bool Genesis::InstallExperimentalNatives() {
                "native harmony-array.js") == 0) {
       if (!CompileExperimentalBuiltin(isolate(), i)) return false;
     }
+    if (FLAG_harmony_maths &&
+        strcmp(ExperimentalNatives::GetScriptName(i).start(),
+               "native harmony-math.js") == 0) {
+      if (!CompileExperimentalBuiltin(isolate(), i)) return false;
+    }
   }
 
   InstallExperimentalNativeFunctions();