ART: Allow scoped adjustments to log verbosity

Add ScopedLogSeverity to adjust the logging level.

Suppress warnings by default in gtests. Suppress errors in instances
where errors are expected.

Change-Id: If3ef865813e9505ab60bc90baed63ff11d90afbb
diff --git a/runtime/indirect_reference_table_test.cc b/runtime/indirect_reference_table_test.cc
index 99ee597..1156cf5 100644
--- a/runtime/indirect_reference_table_test.cc
+++ b/runtime/indirect_reference_table_test.cc
@@ -43,6 +43,9 @@
 }
 
 TEST_F(IndirectReferenceTableTest, BasicTest) {
+  // This will lead to error messages in the log.
+  ScopedLogSeverity sls(LogSeverity::FATAL);
+
   ScopedObjectAccess soa(Thread::Current());
   static const size_t kTableInitial = 10;
   static const size_t kTableMax = 20;