Fix layer blending bug

Cached layers were sometimes retaining an obsolete blending
value, causing artifacts where translucent objects were disappearing
completely. Also, added extra tracing info for DisplayLists.

Issue #6303668 Flickering views during SwipeHelper drag

Change-Id: I66ce158652c4a3ed316040585b40b1744e1fad0c
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 06928df..ebb8eb7 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -520,6 +520,7 @@
     layer->texCoords.set(0.0f, bounds.getHeight() / float(layer->getHeight()),
             bounds.getWidth() / float(layer->getWidth()), 0.0f);
     layer->setColorFilter(mColorFilter);
+    layer->setBlend(true);
 
     // Save the layer in the snapshot
     snapshot->flags |= Snapshot::kFlagIsLayer;
@@ -1058,6 +1059,10 @@
     return !mSnapshot->clipRect->isEmpty();
 }
 
+Rect* OpenGLRenderer::getClipRect() {
+    return mSnapshot->clipRect;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Drawing commands
 ///////////////////////////////////////////////////////////////////////////////