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

Blink now supports DCHECK()s and NOTREACHED(), this CL
uses them instead of ASSERT() and ASSERT_NOT_REACHED(),
respectively.

I was going to do the same HTMLCanvasElementCapture, but
removed the DCHECK instead bc of Chrome StyleGuide [1]:
> you should not handle DCHECK() failures, even if failure would
> result in a crash. Attempting to handle a DCHECK() failure is a
> statement that the DCHECK() can fail, which contradicts the point
> of writing the DCHECK(). In particular, do not write code like
> the following:
>
>  DCHECK(foo);
>  if (!foo) ...  // Can't succeed!

BUG=596760

[1] https://www.chromium.org/developers/coding-style#TOC-CHECK-DCHECK-and-NOTREACHED-

Review URL: https://codereview.chromium.org/1861963004

Cr-Commit-Position: refs/heads/master@{#385515}

third_party/WebKit/Source/modules/mediacapturefromelement/HTMLCanvasElementCapture.cpp

@@ -42,13 +42,13 @@ MediaStream* HTMLCanvasElementCapture::captureStream(HTMLCanvasElement& element,
     }
 
     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;

third_party/WebKit/Source/modules/mediarecorder/MediaRecorder.cpp

@@ -38,7 +38,7 @@ String stateToString(MediaRecorder::State state)
         return "paused";
     }
 
-    ASSERT_NOT_REACHED();
+    NOTREACHED();
     return String();
 }
 
@@ -88,7 +88,7 @@ void AllocateVideoAndAudioBitrates(ExceptionState& exceptionState, ExecutionCont
                 audioBps = kSmallestPossibleOpusBitRate;
             }
         } else {
-            ASSERT(!audioBps);
+            DCHECK(!audioBps);
         }
     }
 
@@ -103,7 +103,7 @@ void AllocateVideoAndAudioBitrates(ExceptionState& exceptionState, ExecutionCont
                 videoBps = kSmallestPossibleVpxBitRate;
             }
         } else {
-            ASSERT(!videoBps);
+            DCHECK(!videoBps);
         }
     }
 
@@ -143,10 +143,10 @@ MediaRecorder::MediaRecorder(ExecutionContext* context, MediaStream* stream, con
     , m_state(State::Inactive)
     , m_dispatchScheduledEventRunner(AsyncMethodRunner<MediaRecorder>::create(this, &MediaRecorder::dispatchScheduledEvent))
 {
-    ASSERT(m_stream->getTracks().size());
+    DCHECK(m_stream->getTracks().size());
 
     m_recorderHandler = adoptPtr(Platform::current()->createMediaRecorderHandler());
-    ASSERT(m_recorderHandler);
+    DCHECK(m_recorderHandler);
 
     if (!m_recorderHandler) {
         exceptionState.throwDOMException(NotSupportedError, "No MediaRecorder handler can be created.");
@@ -323,7 +323,7 @@ void MediaRecorder::createBlobEvent(Blob* blob)
 
 void MediaRecorder::stopRecording()
 {
-    ASSERT(m_state != State::Inactive);
+    DCHECK(m_state != State::Inactive);
     m_state = State::Inactive;
 
     m_recorderHandler->stop();