[es2015] Precompute the descriptive string for symbols.

src/builtins/arm64/builtins-arm64.cc

Index: src/builtins/arm64/builtins-arm64.cc
diff --git a/src/builtins/arm64/builtins-arm64.cc b/src/builtins/arm64/builtins-arm64.cc
index 7e96dc4fb3658f52886ad35af4050a7d753008cf..0e286fca696de390e5cfe13aac000699de4b17d7 100644
--- a/src/builtins/arm64/builtins-arm64.cc
+++ b/src/builtins/arm64/builtins-arm64.cc
@@ -298,12 +298,8 @@ void Builtins::Generate_StringConstructor(MacroAssembler* masm) {
 
   // 3b. Convert symbol in x0 to a string.
   __ Bind(&symbol_descriptive_string);
-  {
-    __ Drop(x2);
-    __ Drop(1);
-    __ Push(x0);
-    __ TailCallRuntime(Runtime::kSymbolDescriptiveString);
-  }
+  __ Ldr(x0, FieldMemOperand(x0, Symbol::kDescriptiveStringOffset));
+  // Fall through.
 
   __ bind(&drop_frame_and_ret);
   {