Inline String.fromCharCode in hydrogen.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 7e7d6d5d585759f01f74b5f9cfef0b5f979669d8..3fd5f6dc043ba141edf3a2092ac91e27637a334b 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -2417,11 +2417,9 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateJSGeneratorObject) {
 
 MUST_USE_RESULT static MaybeObject* CharFromCode(Isolate* isolate,
                                                  Object* char_code) {
-  uint32_t code;
-  if (char_code->ToArrayIndex(&code)) {
-    if (code <= 0xffff) {
-      return isolate->heap()->LookupSingleCharacterStringFromCode(code);
-    }
+  if (char_code->IsNumber()) {
+    return isolate->heap()->LookupSingleCharacterStringFromCode(
+        NumberToUint32(char_code) & 0xffff);
   }
   return isolate->heap()->empty_string();
 }