MediaRecorder: ASSERT-->DCHECK and a tiny cleanup in CanvasCapture

third_party/WebKit/Source/modules/mediacapturefromelement/HTMLCanvasElementCapture.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 "modules/mediacapturefromelement/HTMLCanvasElementCapture.h"
 
 #include "core/dom/ExceptionCode.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "modules/mediacapturefromelement/CanvasCaptureMediaStreamTrack.h"
 #include "modules/mediastream/MediaStream.h"
@@ skipping 24 matching lines @@
 }
 
 MediaStream* HTMLCanvasElementCapture::captureStream(HTMLCanvasElement& element, bool givenFrameRate, double frameRate, ExceptionState& exceptionState)
 {
     if (!element.originClean()) {
         exceptionState.throwSecurityError("Canvas is not origin-clean.");
         return nullptr;
     }
 
     WebMediaStreamTrack track;
-    WebSize size(element.width(), element.height());
+    const WebSize size(element.width(), element.height());
     OwnPtr<WebCanvasCaptureHandler> handler;
     if (givenFrameRate)
         handler = adoptPtr(Platform::current()->createCanvasCaptureHandler(size, frameRate, &track));
     else
         handler = adoptPtr(Platform::current()->createCanvasCaptureHandler(size, kDefaultFrameRate, &track));
-    ASSERT(handler);
+
     if (!handler) {
         exceptionState.throwDOMException(NotSupportedError, "No CanvasCapture handler can be created.");
         return nullptr;
     }
 
     CanvasCaptureMediaStreamTrack* canvasTrack;
     if (givenFrameRate)
         canvasTrack = CanvasCaptureMediaStreamTrack::create(track, &element, handler.release(), frameRate);
     else
         canvasTrack = CanvasCaptureMediaStreamTrack::create(track, &element, handler.release());
     // We want to capture a frame in the beginning.
     canvasTrack->requestFrame();
 
     MediaStreamTrackVector tracks;
     tracks.append(canvasTrack);
     return MediaStream::create(element.getExecutionContext(), tracks);
 }
 
 } // namespace blink