Account for empty stack trace with non-empty async chain in V8Initializer.

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

Index: third_party/WebKit/Source/bindings/core/v8/ScriptCallStack.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScriptCallStack.cpp b/third_party/WebKit/Source/bindings/core/v8/ScriptCallStack.cpp
index 90c0ebde9e08a64ee672a3b9a1790785ab8ca766..12ac6517448d8eee7cf0cf67bf17c3b95bd9f01b 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ScriptCallStack.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/ScriptCallStack.cpp
@@ -45,7 +45,8 @@ PassRefPtr<ScriptCallStack> ScriptCallStack::create(v8::Isolate* isolate, v8::Lo
     V8PerIsolateData* data = V8PerIsolateData::from(isolate);
     if (!data->threadDebugger())
         return nullptr;
-    return adoptRef(new ScriptCallStack(data->threadDebugger()->debugger()->createStackTrace(stackTrace, maxStackSize)));
+    OwnPtr<V8StackTrace> stack = data->threadDebugger()->debugger()->createStackTrace(stackTrace, maxStackSize);
+    return stack ? adoptRef(new ScriptCallStack(std::move(stack))) : nullptr;
 }
 
 PassRefPtr<ScriptCallStack> ScriptCallStack::capture(size_t maxStackSize)