Fix z-order for webview surface control

Set the root surface control transparent, and set the z order of the newly created child surface control to -1.
A new callback is needed to update root surface control in sync from Java side.

Bug: 186750329
Test: use latest APKs from Webview team, play a video, mini toolbar should be visible
Change-Id: I0b37ee8f83fd2b41ff4f2856dbadd31ff6170baf
diff --git a/libs/hwui/renderthread/RenderThread.h b/libs/hwui/renderthread/RenderThread.h
index dd06009..c5e3746 100644
--- a/libs/hwui/renderthread/RenderThread.h
+++ b/libs/hwui/renderthread/RenderThread.h
@@ -96,6 +96,8 @@
 typedef void (*AST_apply)(ASurfaceTransaction* transaction);
 typedef void (*AST_setVisibility)(ASurfaceTransaction* transaction,
                                   ASurfaceControl* surface_control, int8_t visibility);
+typedef void (*AST_setZOrder)(ASurfaceTransaction* transaction, ASurfaceControl* surface_control,
+                              int32_t z_order);
 
 struct ASurfaceControlFunctions {
     ASurfaceControlFunctions();
@@ -112,6 +114,7 @@
     AST_delete transactionDeleteFunc;
     AST_apply transactionApplyFunc;
     AST_setVisibility transactionSetVisibilityFunc;
+    AST_setZOrder transactionSetZOrderFunc;
 };
 
 class ChoreographerSource;