Add FieldValue.boolean_value() (#862)

Author: rsgowman

Firestore/core/src/firebase/firestore/model/field_value.h

@@ -96,6 +96,11 @@ class FieldValue {
     return tag_;
   }
 
+  bool boolean_value() const {
+    FIREBASE_ASSERT(tag_ == Type::Boolean);
+    return boolean_value_;
+  }
+
   int64_t integer_value() const {
     FIREBASE_ASSERT(tag_ == Type::Integer);
     return integer_value_;

Firestore/core/src/firebase/firestore/remote/serializer.cc

@@ -131,12 +131,7 @@ void Serializer::EncodeFieldValue(const FieldValue& field_value,
         // TODO(rsgowman): figure out error handling
         abort();
       }
-      if (field_value == FieldValue::TrueValue()) {
-        EncodeBool(&stream, true);
-      } else {
-        FIREBASE_DEV_ASSERT(field_value == FieldValue::FalseValue());
-        EncodeBool(&stream, false);
-      }
+      EncodeBool(&stream, field_value.boolean_value());
       break;
 
     case FieldValue::Type::Integer: