add tracepoint for when the display chain is stuffed

bug 30173296

Change-Id: I7845542d4e5c19ccb7c3ee6498cc2d70278b5397
diff --git a/libs/hwui/renderthread/CanvasContext.cpp b/libs/hwui/renderthread/CanvasContext.cpp
index 5003c6a..bfcb0e5 100644
--- a/libs/hwui/renderthread/CanvasContext.cpp
+++ b/libs/hwui/renderthread/CanvasContext.cpp
@@ -234,6 +234,7 @@
     }
 
     // All signs point to a stuffed swap chain
+    ATRACE_NAME("swap chain stuffed");
     return true;
 }