Opt compiler: Add a description to slow paths.

Change-Id: I22160d90de3fe0ab3e6a2acc440bda8daa00e0f0
diff --git a/compiler/optimizing/intrinsics_arm64.cc b/compiler/optimizing/intrinsics_arm64.cc
index c108ad5..8bcb88b 100644
--- a/compiler/optimizing/intrinsics_arm64.cc
+++ b/compiler/optimizing/intrinsics_arm64.cc
@@ -130,6 +130,8 @@
     __ B(GetExitLabel());
   }
 
+  const char* GetDescription() const OVERRIDE { return "IntrinsicSlowPathARM64"; }
+
  private:
   // The instruction where this slow path is happening.
   HInvoke* const invoke_;