Rewrite media::Pipeline state transition machinery.

media/base/media_log.cc

Index: media/base/media_log.cc
diff --git a/media/base/media_log.cc b/media/base/media_log.cc
index d52c24b712ce181f3377def5dfe1da136e2b786a..fbb769e03c0a4ce1f151bad904b75f8e64c94177 100644
--- a/media/base/media_log.cc
+++ b/media/base/media_log.cc
@@ -81,14 +81,10 @@ const char* MediaLog::PipelineStateToString(Pipeline::State state) {
       return "starting";
     case Pipeline::kStarted:
       return "started";
-    case Pipeline::kEnded:
-      return "ended";
     case Pipeline::kStopping:
       return "stopping";
     case Pipeline::kStopped:
       return "stopped";
-    case Pipeline::kError:
-      return "error";
   }
   NOTREACHED();
   return NULL;