Fix memory leak in verifier.

We create std::ostringstream objects for failure messages but it appears we did
not delete them upon destruction. This CL fixes this.

Change-Id: If95c6f1b154db9c1d49ade4c1384ef6015663419
(cherry picked from commit 33691abbc43850fd2b2951256c4b6bbc9733ccc8)
diff --git a/runtime/verifier/method_verifier.h b/runtime/verifier/method_verifier.h
index 5c06cd5..e541096 100644
--- a/runtime/verifier/method_verifier.h
+++ b/runtime/verifier/method_verifier.h
@@ -230,6 +230,10 @@
                  uint32_t access_flags, bool can_load_classes, bool allow_soft_failures)
           SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
+  ~MethodVerifier() {
+    STLDeleteElements(&failure_messages_);
+  }
+
   // Run verification on the method. Returns true if verification completes and false if the input
   // has an irrecoverable corruption.
   bool Verify() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);