ObjC: Implement HW codecs in ObjC instead of C++

The current ObjC HW encoder is implemented as a C++
webrtc::VideoEncoder. We then wrap it two times in the following way:
webrtc::VideoEncoder -> RTCVideoEncoder -> webrtc::VideoEncoder.
This was originally done to minimize the code diff when landing the
injectable encoder.

This CL removes the first wrapping and implements the ObjC HW encoder
as a RTCVideoEncoder directly. Similarly, the decoder is implemented
as a RTCVideoDecoder directly.

Based on andersc@ CL: https://codereview.webrtc.org/2978623002/.

BUG=webrtc:7924

Review-Url: https://codereview.webrtc.org/2987413002
Cr-Commit-Position: refs/heads/master@{#19255}

webrtc/sdk/objc/Framework/Classes/VideoToolbox/helpers.h

@@ -0,0 +1,47 @@
+/*
+ *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ *
+ */
+
+#ifndef WEBRTC_SDK_OBJC_FRAMEWORK_CLASSES_VIDEOTOOLBOX_HELPERS_H_
+#define WEBRTC_SDK_OBJC_FRAMEWORK_CLASSES_VIDEOTOOLBOX_HELPERS_H_
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <VideoToolbox/VideoToolbox.h>
+#include <string>
+
+// Convenience function for creating a dictionary.
+inline CFDictionaryRef CreateCFTypeDictionary(CFTypeRef* keys,
+                                              CFTypeRef* values,
+                                              size_t size) {
+  return CFDictionaryCreate(kCFAllocatorDefault, keys, values, size,
+                            &kCFTypeDictionaryKeyCallBacks,
+                            &kCFTypeDictionaryValueCallBacks);
+}
+
+// Copies characters from a CFStringRef into a std::string.
+std::string CFStringToString(const CFStringRef cf_string);
+
+// Convenience function for setting a VT property.
+void SetVTSessionProperty(VTSessionRef session, CFStringRef key, int32_t value);
+
+// Convenience function for setting a VT property.
+void SetVTSessionProperty(VTSessionRef session,
+                          CFStringRef key,
+                          uint32_t value);
+
+// Convenience function for setting a VT property.
+void SetVTSessionProperty(VTSessionRef session, CFStringRef key, bool value);
+
+// Convenience function for setting a VT property.
+void SetVTSessionProperty(VTSessionRef session,
+                          CFStringRef key,
+                          CFStringRef value);
+
+#endif  // WEBRTC_SDK_OBJC_FRAMEWORK_CLASSES_VIDEOTOOLBOX_HELPERS_H_