src: internalize per-isolate string properties

Speeds up property lookups a little and it creates the string in the
old space straight away.  It's a little easier on the garbage collector
because it doesn't have to track eternalized strings in the new space.

PR-URL: https://github.com/nodejs/node/pull/3060
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

src/env-inl.h

@@ -36,12 +36,26 @@ inline void Environment::IsolateData::Put() {
   }
 }
 
+// Create string properties as internalized one byte strings.
+//
+// Internalized because it makes property lookups a little faster and because
+// the string is created in the old space straight away.  It's going to end up
+// in the old space sooner or later anyway but now it doesn't go through
+// v8::Eternal's new space handling first.
+//
+// One byte because our strings are ASCII and we can safely skip V8's UTF-8
+// decoding step.  It's a one-time cost, but why pay it when you don't have to?
 inline Environment::IsolateData::IsolateData(v8::Isolate* isolate,
                                              uv_loop_t* loop)
     : event_loop_(loop),
       isolate_(isolate),
 #define V(PropertyName, StringValue)                                          \
-    PropertyName ## _(isolate, FIXED_ONE_BYTE_STRING(isolate, StringValue)),
+    PropertyName ## _(isolate,                                                \
+                      v8::String::NewFromOneByte(                             \
+                          isolate,                                            \
+                          reinterpret_cast<const uint8_t*>(StringValue),      \
+                          v8::NewStringType::kInternalized,                   \
+                          sizeof(StringValue) - 1).ToLocalChecked()),
     PER_ISOLATE_STRING_PROPERTIES(V)
 #undef V
     ref_count_(0) {}

src/env.h

@@ -39,7 +39,7 @@ namespace node {
 #endif
 
 // Strings are per-isolate primitives but Environment proxies them
-// for the sake of convenience.
+// for the sake of convenience.  Strings should be ASCII-only.
 #define PER_ISOLATE_STRING_PROPERTIES(V)                                      \
   V(address_string, "address")                                                \
   V(args_string, "args")                                                      \