Reimplement Number.prototype.toString with non-default radix.

src/builtins/builtins-number.cc

Index: src/builtins/builtins-number.cc
diff --git a/src/builtins/builtins-number.cc b/src/builtins/builtins-number.cc
index a63066cfbd7857b42cdf99db8d646f68feae2b6b..cddfe241e2f78de0e195ba7a6b58f163a1055aaa 100644
--- a/src/builtins/builtins-number.cc
+++ b/src/builtins/builtins-number.cc
@@ -545,7 +545,8 @@ BUILTIN(NumberPrototypeToString) {
   }
 
   // Fast case where the result is a one character string.
-  if (IsUint32Double(value_number) && value_number < radix_number) {
+  if ((IsUint32Double(value_number) && value_number < radix_number) ||
+      value_number == -0.0) {

[Jakob Kummerow, 2016/11/28 12:15:11]

DBC: This is misleading, because "value_number == -0.0" also evaluates to true
when value_number == 0.0. That's fine here, but could lead to bugs when this
pattern is copied elsewhere.

Use IsMinusZero() from conversions.h to actually check for -0, or compare
against 0.0 with a comment like "Covers both 0 and -0." to make explicit what's
going on.

[Yang, 2016/11/28 12:20:21]

Noted. I originally had compared to 0.0 in patch set 1.

     // Character array used for conversion.
     static const char kCharTable[] = "0123456789abcdefghijklmnopqrstuvwxyz";
     return *isolate->factory()->LookupSingleCharacterStringFromCode(