Implement Optional::has_value() and Optional::reset().

base/optional.h

Index: base/optional.h
diff --git a/base/optional.h b/base/optional.h
index b468964ae339fbead38f769dd315ff39a008d054..98cd95857094023fae865137d7b90838a93d986f 100644
--- a/base/optional.h
+++ b/base/optional.h
@@ -163,6 +163,8 @@ class Optional {
 
   constexpr explicit operator bool() const { return !storage_.is_null_; }
 
+  constexpr bool has_value() const { return !storage_.is_null_; }
+
   // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
   // meant to be 'constexpr const'.
   T& value() & {
@@ -231,6 +233,10 @@ class Optional {
     swap(**this, *other);
   }
 
+  void reset() {
+    FreeIfNeeded();
+  }
+
   template <class... Args>
   void emplace(Args&&... args) {
     FreeIfNeeded();