Handle OffscreenCanvas.convertToBlob exceptions: EncodingError & InvalidStateError

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

 // Copyright 2015 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.
 
 #include "core/offscreencanvas/OffscreenCanvas.h"
 
 #include "core/dom/ExceptionCode.h"
 #include "core/fileapi/Blob.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/html/ImageData.h"
@@ skipping 287 matching lines @@
 
   double startTime = WTF::monotonicallyIncreasingTime();
   String encodingMimeType = ImageEncoderUtils::toEncodingMimeType(
       options.type(), ImageEncoderUtils::EncodeReasonConvertToBlobPromise);
 
   ImageData* imageData = nullptr;
   if (this->renderingContext()) {
     imageData = this->renderingContext()->toImageData(SnapshotReasonUnknown);
   }
   if (!imageData) {
-    return ScriptPromise();
+    exceptionState.throwDOMException(
+        InvalidStateError, "OffscreenCanvas object has no rendering contexts");
+    return exceptionState.reject(scriptState);
   }
 
   ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
 
   Document* document =
       scriptState->getExecutionContext()->isDocument()
           ? static_cast<Document*>(scriptState->getExecutionContext())
           : nullptr;
 
   CanvasAsyncBlobCreator* asyncCreator = CanvasAsyncBlobCreator::create(
       imageData->data(), encodingMimeType, imageData->size(), startTime,
       document, resolver);
 
   asyncCreator->scheduleAsyncBlobCreation(options.quality());
 
   return resolver->promise();
 }
 
 DEFINE_TRACE(OffscreenCanvas) {
   visitor->trace(m_context);
   visitor->trace(m_executionContext);
   visitor->trace(m_commitPromiseResolver);
   EventTargetWithInlineData::trace(visitor);
 }
 
 }  // namespace blink