Make delete API consistent for String objects

Deleting an in-bounds character index from a String object should always return
false.

BUG=
LOG=N

Review URL: https://codereview.chromium.org/1153673003

Cr-Commit-Position: refs/heads/master@{#28592}

src/api.cc

@@ -3477,7 +3477,7 @@ i::MaybeHandle<i::Object> DeleteObjectProperty(
     // underlying string does nothing with the deletion, we can ignore
     // such deletions.
     if (receiver->IsStringObjectWithCharacterAt(index)) {
-      return isolate->factory()->true_value();
+      return isolate->factory()->false_value();
     }
 
     return i::JSReceiver::DeleteElement(receiver, index, language_mode);

test/cctest/test-api.cc

@@ -1590,6 +1590,17 @@ THREADED_TEST(StringObject) {
 }
 
 
+TEST(StringObjectDelete) {
+  LocalContext context;
+  v8::HandleScope scope(context->GetIsolate());
+  v8::Handle<Value> boxed_string = CompileRun("new String(\"test\")");
+  CHECK(boxed_string->IsStringObject());
+  v8::Handle<v8::Object> str_obj = boxed_string.As<v8::Object>();
+  CHECK(!str_obj->Delete(2));
+  CHECK(!str_obj->Delete(v8_num(2)));
+}
+
+
 THREADED_TEST(NumberObject) {
   LocalContext env;
   v8::HandleScope scope(env->GetIsolate());