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/base/logging.cc b/runtime/base/logging.cc
index f3e0918..0764b87 100644
--- a/runtime/base/logging.cc
+++ b/runtime/base/logging.cc
@@ -303,4 +303,13 @@
 #endif
 }
 
+ScopedLogSeverity::ScopedLogSeverity(LogSeverity level) {
+  old_ = gMinimumLogSeverity;
+  gMinimumLogSeverity = level;
+}
+
+ScopedLogSeverity::~ScopedLogSeverity() {
+  gMinimumLogSeverity = old_;
+}
+
 }  // namespace art