Injectable software codecs for Android.

This is similar to https://webrtc-review.googlesource.com/c/src/+/3620
for iOS.

Using the new WebRtcMediaEngineFactory::Create API, the built-in
software video codecs are no longer appended to the injected codecs.

To be able to use the software codecs, they are exposed as Java
classes through SoftwareVideoEncoderFactory etc.

There is also a new DefaultVideoEncoderFactory used by AppRTCMobile.
This factory tries to use hardware implementations where available,
but falls back to using the injected software codecs.

The HardwareVideoEncoderFactory is temporarily also falling back on
the software codecs in its default configuration in order to
maintain backwards compatibility.

Bug: webrtc:7925
Change-Id: I3e8c5ed492ccd160aca968986ad217d7978a951c
Reviewed-on: https://webrtc-review.googlesource.com/17480
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20647}

sdk/android/api/org/webrtc/DefaultVideoDecoderFactory.java

@@ -0,0 +1,31 @@
+/*
+ *  Copyright 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.
+ */
+
+package org.webrtc;
+
+public class DefaultVideoDecoderFactory implements VideoDecoderFactory {
+  private final HardwareVideoDecoderFactory hardwareVideoDecoderFactory;
+  private final SoftwareVideoDecoderFactory softwareVideoDecoderFactory;
+
+  public DefaultVideoDecoderFactory(EglBase.Context eglContext) {
+    hardwareVideoDecoderFactory =
+        new HardwareVideoDecoderFactory(eglContext, false /* fallbackToSoftware */);
+    softwareVideoDecoderFactory = new SoftwareVideoDecoderFactory();
+  }
+
+  @Override
+  public VideoDecoder createDecoder(String codecType) {
+    VideoDecoder decoder = hardwareVideoDecoderFactory.createDecoder(codecType);
+    if (decoder != null) {
+      return decoder;
+    }
+    return softwareVideoDecoderFactory.createDecoder(codecType);
+  }
+}