Add DCHECKs to check that toV8 never returns an empty handle

third_party/WebKit/Source/bindings/core/v8/ToV8.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ToV8_h
 #define ToV8_h
 
 // toV8() provides C++ -> V8 conversion. Note that toV8() can return an empty
 // handle. Call sites must check IsEmpty() before using return value.
 
@@ skipping 19 matching lines @@
 // ScriptWrappable
 
 inline v8::Local<v8::Value> toV8(ScriptWrappable* impl, v8::Local<v8::Object> creationContext, v8::Isolate* isolate)
 {
     if (UNLIKELY(!impl))
         return v8::Null(isolate);
     v8::Local<v8::Value> wrapper = DOMDataStore::getWrapper(impl, isolate);
     if (!wrapper.IsEmpty())
         return wrapper;
 
-    return impl->wrap(isolate, creationContext);
+    wrapper = impl->wrap(isolate, creationContext);
+    DCHECK(!wrapper.IsEmpty());
+    return wrapper;
 }
 
 inline v8::Local<v8::Value> toV8(Node* impl, v8::Local<v8::Object> creationContext, v8::Isolate* isolate)
 {
     if (UNLIKELY(!impl))
         return v8::Null(isolate);
     v8::Local<v8::Value> wrapper = DOMDataStore::getWrapper(impl, isolate);
     if (!wrapper.IsEmpty())
         return wrapper;
 
-    return ScriptWrappable::fromNode(impl)->wrap(isolate, creationContext);
+    wrapper = ScriptWrappable::fromNode(impl)->wrap(isolate, creationContext);
+    DCHECK(!wrapper.IsEmpty());
+    return wrapper;
 }
 
 // Special versions for DOMWindow, WorkerOrWorkletGlobalScope and EventTarget
 
 CORE_EXPORT v8::Local<v8::Value> toV8(DOMWindow*, v8::Local<v8::Object> creationContext, v8::Isolate*);
 CORE_EXPORT v8::Local<v8::Value> toV8(EventTarget*, v8::Local<v8::Object> creationContext, v8::Isolate*);
 v8::Local<v8::Value> toV8(WorkerOrWorkletGlobalScope*, v8::Local<v8::Object> creationContext, v8::Isolate*);
 
 // PassRefPtr and RefPtr
 
@@ skipping 211 matching lines @@
 // Cannot define in ScriptValue because of the circular dependency between toV8 and ScriptValue
 template<typename T>
 inline ScriptValue ScriptValue::from(ScriptState* scriptState, T&& value)
 {
     return ScriptValue(scriptState, toV8(std::forward<T>(value), scriptState));
 }
 
 } // namespace blink
 
 #endif // ToV8_h