Traverse layers in update order

bug:8540150

Layers now require traversal in update order, as it will be child
first, then parent for layer-in-layer

Fixes issue with deferred layer playback not flushing in order, and
thus child not painting before parent

Also fixes DisplayList to only be cleared after flush in deferred list

Change-Id: I2f284d00079cdb20798aeef6a1c94e823940db40
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 1138998..d34246d 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -571,8 +571,8 @@
             startMark("Defer Layer Updates");
         }
 
-        // Note: it is very important to update the layers in reverse order
-        for (int i = count - 1; i >= 0; i--) {
+        // Note: it is very important to update the layers in order
+        for (int i = 0; i < count; i++) {
             Layer* layer = mLayerUpdates.itemAt(i);
             updateLayer(layer, false);
             if (CC_UNLIKELY(mCaches.drawDeferDisabled)) {
@@ -594,8 +594,8 @@
         startMark("Apply Layer Updates");
         char layerName[12];
 
-        // Note: it is very important to update the layers in reverse order
-        for (int i = count - 1; i >= 0; i--) {
+        // Note: it is very important to update the layers in order
+        for (int i = 0; i < count; i++) {
             sprintf(layerName, "Layer #%d", i);
             startMark(layerName);