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.h b/runtime/base/logging.h
index ae83e33..cc1a4a1 100644
--- a/runtime/base/logging.h
+++ b/runtime/base/logging.h
@@ -254,6 +254,16 @@
   DISALLOW_COPY_AND_ASSIGN(LogMessage);
 };
 
+// Allows to temporarily change the minimum severity level for logging.
+class ScopedLogSeverity {
+ public:
+  explicit ScopedLogSeverity(LogSeverity level);
+  ~ScopedLogSeverity();
+
+ private:
+  LogSeverity old_;
+};
+
 }  // namespace art
 
 #endif  // ART_RUNTIME_BASE_LOGGING_H_