Remove "mixin" from BeginFrameSource/Observer base classes.

cc/scheduler/begin_frame_source.cc

Index: cc/scheduler/begin_frame_source.cc
diff --git a/cc/scheduler/begin_frame_source.cc b/cc/scheduler/begin_frame_source.cc
index 48d834359f43d41fd25b572ce387964f49ee9121..2e7ef0633ac365e55a6ea438246e17185e602307 100644
--- a/cc/scheduler/begin_frame_source.cc
+++ b/cc/scheduler/begin_frame_source.cc
@@ -28,16 +28,16 @@
 
 namespace cc {
 
-// BeginFrameObserverMixIn -----------------------------------------------
-BeginFrameObserverMixIn::BeginFrameObserverMixIn()
+// BeginFrameObserverBase -----------------------------------------------
+BeginFrameObserverBase::BeginFrameObserverBase()
     : last_begin_frame_args_(), dropped_begin_frame_args_(0) {
 }
 
-const BeginFrameArgs BeginFrameObserverMixIn::LastUsedBeginFrameArgs() const {
+const BeginFrameArgs BeginFrameObserverBase::LastUsedBeginFrameArgs() const {
   return last_begin_frame_args_;
 }
-void BeginFrameObserverMixIn::OnBeginFrame(const BeginFrameArgs& args) {
-  DEBUG_FRAMES("BeginFrameObserverMixIn::OnBeginFrame",
+void BeginFrameObserverBase::OnBeginFrame(const BeginFrameArgs& args) {
+  DEBUG_FRAMES("BeginFrameObserverBase::OnBeginFrame",
                "last args",
                last_begin_frame_args_.AsValue(),
                "new args",
@@ -52,7 +52,7 @@ void BeginFrameObserverMixIn::OnBeginFrame(const BeginFrameArgs& args) {
   }
 }
 
-void BeginFrameObserverMixIn::AsValueInto(
+void BeginFrameObserverBase::AsValueInto(
     base::trace_event::TracedValue* dict) const {
   dict->BeginDictionary("last_begin_frame_args_");
   last_begin_frame_args_.AsValueInto(dict);