MediaRecorder Blink part

public/platform/WebMediaRecorderHandlerClient.h

+// 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.
+
+#ifndef WebMediaRecorderHandlerClient_h
+#define WebMediaRecorderHandlerClient_h
+
+#include "WebCommon.h"
+
+namespace blink {
+
+class WebString;
+
+// Interface used by a MediaRecorder to get errors and recorded data delivered.
+class BLINK_PLATFORM_EXPORT WebMediaRecorderHandlerClient {

[Peter Beverloo, 2015/09/01 17:17:12]

I don't think you need BLINK_PLATFORM_EXPORT here. This is what may be causing
your linking error.

[mcasas, 2015/09/02 03:10:18]

I'm afraid Windows is not happy to have MediaRecorder as a 
WebMediaRecorderHandlerClient and not see a .cpp file. Win
compiler doesn't generate an object file at all for the base 
class if it doesn't see a .cpp file. Sad, but I've found it before,
see below. (The /.../ are mine).

e:\b\build\slave\...\source\modules\mediarecorder\mediarecorder.h(25) : error
C2220: warning treated as error - no 'object' file generated
e:\b\build\slave\...\source\modules\mediarecorder\mediarecorder.h(25) : warning
C4275: non dll-interface class 'blink::WebMediaRecorderHandlerClient' used as
base for dll-interface class 'blink::MediaRecorder'

        e:\b\build\slave\...\public\platform\webmediarecorderhandlerclient.h(15)
: see declaration of 'blink::WebMediaRecorderHandlerClient'
        e:\b\build\slave\...\source\modules\mediarecorder\mediarecorder.h(23) :
see declaration of 'blink::MediaRecorder'
ninja: build stopped: subcommand failed.

[Peter Beverloo, 2015/09/02 16:39:37]

What I don't understand is why you need this at all. Did those errors occur
without BLINK_PLATFORM_EXPORT?

To illustrate, the Notification in Source/modules/notifications/Notification.h
implements WebNotificationDelegate which is logically identical to your class.
However, it doesn't need a .cpp file. There are various other examples of this
in Blink as well.

(I've created https://codereview.chromium.org/1311353010 to see if the
destructor might make the difference.)

[mcasas, 2015/09/02 21:01:47]

PS10 removes the .cpp and digs a bit further in the issue, 
thanks for pushing :) -- The problem was the destructor 
coupled with the BLINK_PLATFORM_EXPORT.

I followed your example and DocumentWebSocketChannel,
which is a WebSocketHandleClient and is MODULES_EXPORTed;
the catch is that the base class has no destructor.

+public:
+    virtual void writeData(const char* data, size_t length, bool lastInslice) {}
+
+    virtual void failOutOfMemory(const WebString& message) {}
+    virtual void failIllegalStreamModification(const WebString& message) {}
+    virtual void failOtherRecordingError(const WebString& message) {}

[Peter Beverloo, 2015/09/01 17:17:12]

Since this class shouldn't be instantiated by itself, why not make all these
virtuals, aside from the destructor, pure virtual?

[mcasas, 2015/09/02 03:10:18]

Done.

+
+protected:
+    virtual ~WebMediaRecorderHandlerClient() = default;
+};
+
+} // namespace blink
+
+#endif  // WebMediaRecorderHandlerClient_h