Opt compiler: Add a description to slow paths.

Change-Id: I22160d90de3fe0ab3e6a2acc440bda8daa00e0f0
diff --git a/compiler/optimizing/code_generator.h b/compiler/optimizing/code_generator.h
index 5b0abd7..b1f1674 100644
--- a/compiler/optimizing/code_generator.h
+++ b/compiler/optimizing/code_generator.h
@@ -97,6 +97,8 @@
     return saved_fpu_stack_offsets_[reg];
   }
 
+  virtual const char* GetDescription() const = 0;
+
  protected:
   static constexpr size_t kMaximumNumberOfExpectedRegisters = 32;
   static constexpr uint32_t kRegisterNotSaved = -1;