Add RecordFree to the GarbageCollector interface

RecordFree now calls the Heap::RecordFree as well as updates the
garbage collector's internal bytes freed accounting.

Change-Id: I8cb03748b0768e3c8c50ea709572960e6e4ad219
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index dab668f..4484494 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -1143,13 +1143,13 @@
   GetLiveBitmap()->Walk(Heap::VerificationCallback, this);
 }
 
-void Heap::RecordFree(ssize_t freed_objects, ssize_t freed_bytes) {
+void Heap::RecordFree(uint64_t freed_objects, int64_t freed_bytes) {
   // Use signed comparison since freed bytes can be negative when background compaction foreground
   // transitions occurs. This is caused by the moving objects from a bump pointer space to a
   // free list backed space typically increasing memory footprint due to padding and binning.
-  DCHECK_LE(freed_bytes, static_cast<ssize_t>(num_bytes_allocated_.Load()));
-  DCHECK_GE(freed_objects, 0);
-  num_bytes_allocated_.FetchAndSub(freed_bytes);
+  DCHECK_LE(freed_bytes, static_cast<int64_t>(num_bytes_allocated_.Load()));
+  // Note: This relies on 2s complement for handling negative freed_bytes.
+  num_bytes_allocated_.FetchAndSub(static_cast<ssize_t>(freed_bytes));
   if (Runtime::Current()->HasStatsEnabled()) {
     RuntimeStats* thread_stats = Thread::Current()->GetStats();
     thread_stats->freed_objects += freed_objects;