dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/cps_ir/builtin_operator.dart

Index: pkg/compiler/lib/src/cps_ir/builtin_operator.dart
diff --git a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
index 0995e342cf047a1cece617ff67e4889119deee57..abdda0ac40c16c6c10d952f9821ebd1a1014b35c 100644
--- a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
+++ b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
@@ -37,6 +37,13 @@ enum BuiltinOperator {
   NumGt,
   NumGe,
 
+  /// Concatenates any number of strings.
+  ///
+  /// Takes any number of arguments, and each argument must be a string.
+  ///
+  /// Returns the empty string if no arguments are given.
+  StringConcat,

[karlklose, 2015/06/19 08:33:44]

I would prefer not to abbreviate the enum identifiers - it should not make a big
difference in line length and reads much nicer.

[asgerf, 2015/06/19 11:04:34]

Done.

+
   /// Returns true if the two arguments are the same value, and that value is
   /// not NaN, or if one argument is +0 and the other is -0.
   ///