Remove null support in SharedFileRegion

ParcelFileDescriptor does not support null (negative) file descriptors
so we remove it from SharedFileRegion and expect that a @nullable
SharedFileRegion is used for cases where a null file descriptor is
allowed.

Test: atest shmemTest
Change-Id: Icf226181cf6de9759ed3145ff6b5ad0d8fd650af
diff --git a/media/libshmem/Android.bp b/media/libshmem/Android.bp
index fae98ed..c8d2284 100644
--- a/media/libshmem/Android.bp
+++ b/media/libshmem/Android.bp
@@ -41,6 +41,7 @@
     srcs: ["ShmemTest.cpp"],
     shared_libs: [
         "libbinder",
+        "libcutils",
         "libshmemcompat",
         "libshmemutil",
         "libutils",