Implement rosalloc page trimming without suspending threads.

Also, making it more efficient by not going through the chunks smaller
than the page size by not using InspectAll().

Change-Id: I79ceb0374cb8aba5f6b8dde1afbace9af98b6cff
diff --git a/runtime/gc/space/rosalloc_space.cc b/runtime/gc/space/rosalloc_space.cc
index 012267b..5c5e7f8 100644
--- a/runtime/gc/space/rosalloc_space.cc
+++ b/runtime/gc/space/rosalloc_space.cc
@@ -222,6 +222,7 @@
 }
 
 size_t RosAllocSpace::Trim() {
+  VLOG(heap) << "RosAllocSpace::Trim() ";
   {
     MutexLock mu(Thread::Current(), lock_);
     // Trim to release memory at the end of the space.
@@ -229,10 +230,7 @@
   }
   // Attempt to release pages if it does not release all empty pages.
   if (!rosalloc_->DoesReleaseAllPages()) {
-    VLOG(heap) << "RosAllocSpace::Trim() ";
-    size_t reclaimed = 0;
-    InspectAllRosAlloc(DlmallocMadviseCallback, &reclaimed, false);
-    return reclaimed;
+    return rosalloc_->ReleasePages();
   }
   return 0;
 }