Added %_Likely/%_Unlikely intrinsics (special cases of GCC's __builin_expect).

src/runtime/runtime-internal.cc

Index: src/runtime/runtime-internal.cc
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index 973c204435f7ca24fa17541c1ab6e8219f6eaacb..0e538696fcc1ba69f5dbd660982d1f6bb023fcbd 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -330,5 +330,16 @@ RUNTIME_FUNCTION(Runtime_IncrementStatsCounter) {
   }
   return isolate->heap()->undefined_value();
 }
+
+
+RUNTIME_FUNCTION(Runtime_Likely) {
+  DCHECK(args.length() == 1);
+  return args[0];
+}
+
+
+RUNTIME_FUNCTION(Runtime_Unlikely) {
+  return __RT_impl_Runtime_Likely(args, isolate);
+}
 }
 }  // namespace v8::internal