SurfaceFlinger and libgui: Switch Z-order to signed type.

In preparation for SurfaceFlinger child layers. In that model
children's Z order will be relative to their parent. We need
negative Z values to represent children stacking below their
parent (e.g. SurfaceView). Java side already uses signed types
strangely enough.

Test: Basically a refactoring. SurfaceFlinger still works.
Change-Id: Ifcece69f6f9d917cbf5238a59f8e5de1e8ba6a25
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index f7f9ef5..bb44a36 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -206,7 +206,7 @@
     virtual status_t captureScreen(const sp<IBinder>& display,
             const sp<IGraphicBufferProducer>& producer,
             Rect sourceCrop, uint32_t reqWidth, uint32_t reqHeight,
-            uint32_t minLayerZ, uint32_t maxLayerZ,
+            int32_t minLayerZ, int32_t maxLayerZ,
             bool useIdentityTransform, ISurfaceComposer::Rotation rotation);
     virtual status_t getDisplayStats(const sp<IBinder>& display,
             DisplayStatInfo* stats);
@@ -333,14 +333,14 @@
     void renderScreenImplLocked(
             const sp<const DisplayDevice>& hw,
             Rect sourceCrop, uint32_t reqWidth, uint32_t reqHeight,
-            uint32_t minLayerZ, uint32_t maxLayerZ,
+            int32_t minLayerZ, int32_t maxLayerZ,
             bool yswap, bool useIdentityTransform, Transform::orientation_flags rotation);
 
     status_t captureScreenImplLocked(
             const sp<const DisplayDevice>& hw,
             const sp<IGraphicBufferProducer>& producer,
             Rect sourceCrop, uint32_t reqWidth, uint32_t reqHeight,
-            uint32_t minLayerZ, uint32_t maxLayerZ,
+            int32_t minLayerZ, int32_t maxLayerZ,
             bool useIdentityTransform, Transform::orientation_flags rotation,
             bool isLocalScreenshot);
 
@@ -441,7 +441,7 @@
     void appendSfConfigString(String8& result) const;
     void checkScreenshot(size_t w, size_t s, size_t h, void const* vaddr,
             const sp<const DisplayDevice>& hw,
-            uint32_t minLayerZ, uint32_t maxLayerZ);
+            int32_t minLayerZ, int32_t maxLayerZ);
 
     void logFrameStats();