bindings: Remove duplicate check in ToByteString()

Remove one of the identical copies of the same check from the code, added in
e5bbbb17 ("Bindings: Add ScalarValueString support"). The original check
was added a few days before in 65d50ad9 ("Add ByteString support to IDL
bindings").

R=haraken, jbroman, yukishiino

Change-Id: Ic7cb436200a7c3e15ebd7bd1183c54d16eeae595
Reviewed-on: https://chromium-review.googlesource.com/899183Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#534054}

third_party/WebKit/Source/bindings/core/v8/V8BindingForCore.cpp

@@ -503,6 +503,7 @@ double ToRestrictedDouble(v8::Isolate* isolate,
   return number_value;
 }
 
+// http://heycam.github.io/webidl/#es-ByteString
 String ToByteString(v8::Isolate* isolate,
                     v8::Local<v8::Value> value,
                     ExceptionState& exception_state) {
@@ -510,10 +511,6 @@ String ToByteString(v8::Isolate* isolate,
   if (value.IsEmpty())
     return String();
 
-  // From the Web IDL spec: http://heycam.github.io/webidl/#es-ByteString
-  if (value.IsEmpty())
-    return String();
-
   // 1. Let x be ToString(v)
   v8::Local<v8::String> string_object;
   if (value->IsString()) {