Create frequently used symbols in the vm isolate

vm/snapshot_test.cc

Index: vm/snapshot_test.cc
===================================================================
--- vm/snapshot_test.cc	(revision 9729)
+++ vm/snapshot_test.cc	(working copy)
@@ -10,6 +10,7 @@
 #include "vm/dart_api_message.h"
 #include "vm/dart_api_state.h"
 #include "vm/snapshot.h"
+#include "vm/symbols.h"
 #include "vm/unit_test.h"
 
 namespace dart {
@@ -729,7 +730,7 @@
   String& url = String::Handle(String::New("dart-test:SerializeScript"));
   String& source = String::Handle(String::New(kScriptChars));
   Script& script = Script::Handle(Script::New(url, source, RawScript::kSource));
-  const String& lib_url = String::Handle(String::NewSymbol("TestLib"));
+  const String& lib_url = String::Handle(Symbols::New("TestLib"));
   Library& lib = Library::Handle(Library::New(lib_url));
   lib.Register();
   EXPECT(CompilerTest::TestCompileScript(lib, script));