workaround for an issue where the screen would flicker sometimes

bug: 6020860
Change-Id: I97807db66b66c5f4dcbed0df79d5d257cfc7c0bd
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 6852113..9d821dc 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1000,6 +1000,12 @@
         drawWormhole();
     }
 
+    // FIXME: workaroud for b/6020860
+    glEnable(GL_SCISSOR_TEST);
+    glScissor(0,0,0,0);
+    glClear(GL_COLOR_BUFFER_BIT);
+    // end-workaround
+
     /*
      * and then, render the layers targeted at the framebuffer
      */