Introduce struct MediaConfig, with construction-time settings.

webrtc/media/base/mediaengine.h

Index: webrtc/media/base/mediaengine.h
diff --git a/webrtc/media/base/mediaengine.h b/webrtc/media/base/mediaengine.h
index 017e7b6af5de520081afbabc1851335d694f8c74..89202af7bbac976c14614abdb70cdf9e9483c0f0 100644
--- a/webrtc/media/base/mediaengine.h
+++ b/webrtc/media/base/mediaengine.h
@@ -81,11 +81,13 @@ class MediaEngineInterface {
   // Creates a voice media channel. Returns NULL on failure.
   virtual VoiceMediaChannel* CreateChannel(
       webrtc::Call* call,
+      const MediaConfig& config,
       const AudioOptions& options) = 0;
   // Creates a video media channel, paired with the specified voice channel.
   // Returns NULL on failure.
   virtual VideoMediaChannel* CreateVideoChannel(
       webrtc::Call* call,
+      const MediaConfig& config,
       const VideoOptions& options) = 0;
 
   // Device configuration
@@ -156,12 +158,15 @@ class CompositeMediaEngine : public MediaEngineInterface {
     return voice_.GetAudioState();
   }
   virtual VoiceMediaChannel* CreateChannel(webrtc::Call* call,
+                                           const MediaConfig& config,
                                            const AudioOptions& options) {
-    return voice_.CreateChannel(call, options);
+    return voice_.CreateChannel(call, config, options);
   }
-  virtual VideoMediaChannel* CreateVideoChannel(webrtc::Call* call,
-                                                const VideoOptions& options) {
-    return video_.CreateChannel(call, options);
+  virtual VideoMediaChannel* CreateVideoChannel(
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const VideoOptions& options) {
+    return video_.CreateChannel(call, config, options);
   }
 
   virtual bool GetOutputVolume(int* level) {