[filesapp] Initialize DevToolsLister value_id_

Initialize value_id_ to 0 (spotted by MSAN bots). Note message id 0 is
safe to use: it is never sent by DevToolsListener to chromium devtools
in a CDP command and thus, never in the devtools command response.

Bug: 1113941
Change-Id: I3cfb82464c6d1fffed5d4e653dcfc8968d3df945
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2466572
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Ben Reich <benreich@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816425}

chrome/browser/chromeos/file_manager/devtools_listener.h

@@ -82,7 +82,7 @@ class DevToolsListener : public content::DevToolsAgentHostClient {
 
   base::OnceClosure value_closure_;
   std::unique_ptr<base::DictionaryValue> value_;
-  int value_id_;
+  int value_id_ = 0;
 
   const std::string uuid_;
   bool navigated_ = false;