Move from UniquePtr to std::unique_ptr.

Switch from stlport to libcxx as stlport lacks std::unique_ptr.

Change-Id: I45a3588a8ecf4689521f1df6654ed279a6d0669e
diff --git a/NativeCode.mk b/NativeCode.mk
index 12e8114..b3061aa 100644
--- a/NativeCode.mk
+++ b/NativeCode.mk
@@ -87,7 +87,7 @@
 LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE := libjavacore
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/NativeCode.mk
-include external/stlport/libstlport.mk
+LOCAL_CXX_STL := libc++
 include $(BUILD_SHARED_LIBRARY)
 
 # Test JNI library.
@@ -102,7 +102,7 @@
 LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE := libjavacoretests
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/NativeCode.mk
-include external/stlport/libstlport.mk
+LOCAL_CXX_STL := libc++
 include $(BUILD_SHARED_LIBRARY)
 
 endif # LIBCORE_SKIP_TESTS