Replace StackHandleScopeCollection with VariableSizedHandleScope

VariableSizedHandleScope's internal handle scopes are not pushed
directly on the thread. This means that it is safe to intermix with
other types of handle scopes.

Added test.

Test: clean-oat-host && test-art-host

Change-Id: Id2fd1155788428f394d49615d337d9134824c8f0
diff --git a/compiler/optimizing/optimizing_unit_test.h b/compiler/optimizing/optimizing_unit_test.h
index 2a23c92..58d9017 100644
--- a/compiler/optimizing/optimizing_unit_test.h
+++ b/compiler/optimizing/optimizing_unit_test.h
@@ -90,7 +90,7 @@
 
   {
     ScopedObjectAccess soa(Thread::Current());
-    StackHandleScopeCollection handles(soa.Self());
+    VariableSizedHandleScope handles(soa.Self());
     HGraphBuilder builder(graph, *item, &handles, return_type);
     bool graph_built = (builder.BuildGraph() == kAnalysisSuccess);
     return graph_built ? graph : nullptr;