[chrome.displaySource] Simplify session error types

extensions/common/api/display_source.idl

 // 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.
 
 // The <code>chrome.displaySource</code> API creates a Display
 // session using WebMediaStreamTrack as sources.
 namespace displaySource {
   enum ErrorType {
-    // Cannot create media pipeline from the given media stream which could be
-    // appropriate for a Display session (e.g., necessary codecs are missing
-    // on the platform).
-    create_media_pipeline_error,
-
     // A new Display session cannot be started before the existing one is
     // terminated.
-    exceeded_session_limit_error,
+    session_limit_error,
 
-    // Could not establish connection to the sink.
-    establish_connection_error,
+    // The connection with sink cannot be established or has dropped
+    // unexpectedly.
+    connection_error,
 
     // The capabilities of this Display Source and the connected  
     // sink do not fit (e.g. the sink cannot play the media content of
     // the formats given by the source).
     capabilities_negotiation_error,
 
-    // There was an error while packetizing and sending the media content.
-    media_send_error,
-
-    // The TCP connection with sink has dropped unexpectedly.
-    connection_error,
-
-    // An unexpected message has arrived from the sink.
-    unexpected_message_error,
+    // There was an error in media pipeline: while encoding, packetizing or
+    // sending the media content.
+    media_pipeline_error,
 
     // The sink became unresponsive.
     timeout_error,
 
     // Unspecified error.
     unknown_error
   };
 
   dictionary ErrorInfo {
     ErrorType type;
@@ skipping 103 matching lines @@
     // Event fired when the Display session is terminated.
     // |sinkId| Id of the peer sink
     [nocompile] static void onSessionTerminated(long sinkId);
     // Event fired when an error occurs.
     // |sinkId| Id of the peer sink
     // |errorInfo| error description
     [nocompile] static void onSessionErrorOccured(long sinkId,
                                                   ErrorInfo errorInfo);
   };
 };