Fix gcc build

Change-Id: Ifa0cba98f1781b5d87393def938d74867837257e

src/perfetto_cmd/pbtxt_to_pb.cc

diff --git a/src/perfetto_cmd/pbtxt_to_pb.cc b/src/perfetto_cmd/pbtxt_to_pb.cc
index ec4af7d..cf923d6 100644
--- a/src/perfetto_cmd/pbtxt_to_pb.cc
+++ b/src/perfetto_cmd/pbtxt_to_pb.cc
@@ -405,8 +405,8 @@
   bool saw_colon_for_this_key = false;
   bool saw_semicolon_for_this_value = true;
   bool comment_till_eol = false;
-  Token key;
-  Token value;
+  Token key{};
+  Token value{};
 
   for (size_t i = 0; i < input.size(); i++, column++) {
     bool last_character = i + 1 == input.size();