vm: Add support for changing the scheduler group for a thread.
Also temporarily bumps the scheduler group for background threads while performing GC

Signed-off-by: San Mehat <san@google.com>
diff --git a/vm/Thread.h b/vm/Thread.h
index b64f9b7..86a7845 100644
--- a/vm/Thread.h
+++ b/vm/Thread.h
@@ -398,6 +398,11 @@
 INLINE void dvmSetThreadJNIEnv(Thread* self, JNIEnv* env) { self->jniEnv = env;}
 
 /*
+ * Change the scheduler group of the current process
+ */
+int dvmChangeThreadSchedulerGroup(const char *group);
+
+/*
  * Update the priority value of the underlying pthread.
  */
 void dvmChangeThreadPriority(Thread* thread, int newPriority);