Fix freeId() failed in ~BufferNode

And rename UniqueIdGenerator to BufferHubIdGenerator.

Created a static getter and Use scoped static initialization for
UniqueIdGenerator.

Test: run BufferHubBuffer_test, then "adb logcat | grep bufferhub -i" to
verify that there are no error messages.
Fix: 118844348
Change-Id: Ia75ae4dac13cc709f39161c803401bcbb90c70e2
diff --git a/services/bufferhub/tests/Android.bp b/services/bufferhub/tests/Android.bp
index 8a30ef5..3967886 100644
--- a/services/bufferhub/tests/Android.bp
+++ b/services/bufferhub/tests/Android.bp
@@ -24,10 +24,10 @@
 }
 
 cc_test {
-    name: "UniqueIdGenerator_test",
-    srcs: ["UniqueIdGenerator_test.cpp"],
+    name: "BufferHubIdGenerator_test",
+    srcs: ["BufferHubIdGenerator_test.cpp"],
     cflags: [
-        "-DLOG_TAG=\"UniqueIdGenerator_test\"",
+        "-DLOG_TAG=\"BufferHubIdGenerator_test\"",
         "-DTRACE=0",
         "-DATRACE_TAG=ATRACE_TAG_GRAPHICS",
     ],