Refactor PipelineImpl to use CompositeFilter to manage Filter state transitions.

media/base/mock_filters.cc

Index: media/base/mock_filters.cc
diff --git a/media/base/mock_filters.cc b/media/base/mock_filters.cc
index f2110ffa36da014d3cd2e9b562c3077ab1e5897a..e2d6ad9afdab52636e2bc47b75bf67647ac1325e 100644
--- a/media/base/mock_filters.cc
+++ b/media/base/mock_filters.cc
@@ -20,4 +20,23 @@ void RunStopFilterCallback(FilterCallback* callback) {
   delete callback;
 }
 
+MockFilter::MockFilter() :
+    requires_message_loop_(false) {
+}
+
+MockFilter::MockFilter(bool requires_message_loop) :
+    requires_message_loop_(requires_message_loop) {
+}
+
+MockFilter::~MockFilter() {}
+
+bool MockFilter::requires_message_loop() const {
+  return requires_message_loop_;
+}
+
+const char* MockFilter::message_loop_name() const {
+  return "MockFilter";
+}
+
+
 }  // namespace media