[chrome.displaySource] Implement software based H.264 video encoder.

extensions/renderer/api/display_source/wifi_display/wifi_display_video_encoder.cc

 // Copyright 2016 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 "extensions/renderer/api/display_source/wifi_display/wifi_display_video_encoder.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
 
 namespace extensions {
 
 WiFiDisplayVideoEncoder::InitParameters::InitParameters() = default;
 WiFiDisplayVideoEncoder::InitParameters::InitParameters(const InitParameters&) =
     default;
 WiFiDisplayVideoEncoder::InitParameters::~InitParameters() = default;
 
 WiFiDisplayVideoEncoder::WiFiDisplayVideoEncoder(
     scoped_refptr<base::SingleThreadTaskRunner> media_task_runner)
     : media_task_runner_(std::move(media_task_runner)), send_idr_(false) {
   DCHECK(media_task_runner_);
 }
 
 WiFiDisplayVideoEncoder::~WiFiDisplayVideoEncoder() = default;
 
 // static
 void WiFiDisplayVideoEncoder::Create(
     const InitParameters& params,
     const VideoEncoderCallback& encoder_callback) {
-  CreateVEA(params, encoder_callback);
+  CreateVEA(params, base::Bind(&OnCreatedVEA, params, encoder_callback));
+}
+
+// static
+void WiFiDisplayVideoEncoder::OnCreatedVEA(
+    const InitParameters& params,
+    const VideoEncoderCallback& encoder_callback,
+    scoped_refptr<WiFiDisplayVideoEncoder> vea_encoder) {
+  if (vea_encoder) {
+    // An accelerated encoder was created successfully. Pass it on.
+    encoder_callback.Run(vea_encoder);
+  } else {
+    // An accelerated encoder was not created. Fall back to a software encoder.
+    CreateSVC(params, encoder_callback);
+  }
 }
 
 void WiFiDisplayVideoEncoder::InsertRawVideoFrame(
     const scoped_refptr<media::VideoFrame>& video_frame,
     base::TimeTicks reference_time) {
   DCHECK(!encoded_callback_.is_null());
   media_task_runner_->PostTask(
       FROM_HERE, base::Bind(&WiFiDisplayVideoEncoder::InsertFrameOnMediaThread,
                             this, video_frame, reference_time, send_idr_));
   send_idr_ = false;
 }
 
 void WiFiDisplayVideoEncoder::RequestIDRPicture() {
   send_idr_ = true;
 }
 
 }  // namespace extensions