bindings: Do not get if a dictionary member is missing (3/N)

Bindings is going to update IDL dictionaries to be strict about their
members' existence.  After the update, accessing a getter on a missing
dictionary member will crash.

This CL fixes the potential bug in PerformanceMark's constructor.


Bug: 839389
Change-Id: I1796093b38c00dd876031b44e53d6d983d6d75ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227930
Auto-Submit: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774657}

third_party/blink/renderer/core/timing/performance_mark.cc

@@ -54,7 +54,8 @@ PerformanceMark* PerformanceMark::Create(ScriptState* script_state,
       start = performance->now();
     }
 
-    detail = mark_options->detail();
+    if (mark_options->hasDetail())
+      detail = mark_options->detail();
   } else {
     start = performance->now();
   }
@@ -69,16 +70,13 @@ PerformanceMark* PerformanceMark::Create(ScriptState* script_state,
     return nullptr;
   }
 
-  scoped_refptr<SerializedScriptValue> serialized_detail;
-  if (detail.IsEmpty()) {
-    serialized_detail = SerializedScriptValue::NullValue();
-  } else {
-    serialized_detail = SerializedScriptValue::Serialize(
-        script_state->GetIsolate(), detail.V8Value(),
-        SerializedScriptValue::SerializeOptions(), exception_state);
-    if (exception_state.HadException())
-      return nullptr;
-  }
+  scoped_refptr<SerializedScriptValue> serialized_detail =
+      SerializedScriptValue::Serialize(
+          script_state->GetIsolate(), detail.V8Value(),
+          SerializedScriptValue::SerializeOptions(), exception_state);
+  if (exception_state.HadException())
+    return nullptr;
+
   return MakeGarbageCollected<PerformanceMark>(
       mark_name, start, std::move(serialized_detail), exception_state);
 }