Add colorkey to gl clear operation

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
diff --git a/libs/surfaceflinger/LayerBuffer.cpp b/libs/surfaceflinger/LayerBuffer.cpp
index bd6d472f..8a55a3f 100644
--- a/libs/surfaceflinger/LayerBuffer.cpp
+++ b/libs/surfaceflinger/LayerBuffer.cpp
@@ -600,7 +600,11 @@
 
 void LayerBuffer::OverlaySource::onDraw(const Region& clip) const
 {
-    mLayer.clearWithOpenGL(clip);
+    GLclampx color = 0x000018; //dark blue
+    GLclampx red = 0;
+    GLclampx green = 0;
+    GLclampx blue = 0x1818;
+    mLayer.clearWithOpenGL(clip, red, green, blue, 0);
 }
 
 void LayerBuffer::OverlaySource::onTransaction(uint32_t flags)