Adding 'isolates' argument to LOG to get rid of multiple TLS fetches in profiling.

src/platform-macos.cc

Index: src/platform-macos.cc
diff --git a/src/platform-macos.cc b/src/platform-macos.cc
index 26d1652caba2fd4c108962ef72a3e51c56a35f8b..34152160bbdb80e1e66e8a37866d434710527216 100644
--- a/src/platform-macos.cc
+++ b/src/platform-macos.cc
@@ -150,7 +150,7 @@ void* OS::Allocate(const size_t requested,
                      MAP_PRIVATE | MAP_ANON,
                      kMmapFd, kMmapFdOffset);
   if (mbase == MAP_FAILED) {
-    LOG(StringEvent("OS::Allocate", "mmap failed"));
+    LOG(ISOLATE,StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
   }
   *allocated = msize;