SmbProviderClient: Change mount id to start at 0

Change SmbProviderClient to expect mount_id to start at 0.

CQ-DEPEND=CL:823086

Bug: chromium:757625
Change-Id: I55a13a0e15bf887176825e60c7297827fb45a017
Reviewed-on: https://chromium-review.googlesource.com/823270Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Allen Vicencio <allenvic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523837}

chrome/browser/chromeos/smb_client/smb_service.cc

@@ -50,7 +50,7 @@ void SmbService::OnMountResponse(
     return;
   }
 
-  DCHECK_GT(mount_id, 0);
+  DCHECK_GE(mount_id, 0);
 
   file_system_provider::MountOptions mount_options(options);
   mount_options.file_system_id = base::NumberToString(mount_id);

chromeos/dbus/smb_provider_client.cc

@@ -138,7 +138,7 @@ class SmbProviderClientImpl : public SmbProviderClient {
       return;
     }
     int32_t mount_id = -1;
-    if (!reader.PopInt32(&mount_id) || mount_id <= 0) {
+    if (!reader.PopInt32(&mount_id) || mount_id < 0) {
       DLOG(ERROR) << "Mount: failed to parse mount id";
       std::move(callback).Run(smbprovider::ERROR_DBUS_PARSE_FAILED, -1);
       return;