Revert "extensions: Explicitly ignore result of CalledOnValidThread()."

This reverts commit 7fb8b995.

BUG=417939
TBR=rockot@chromium.org

Review URL: https://codereview.chromium.org/609633002

Cr-Commit-Position: refs/heads/master@{#296845}

extensions/browser/api/hid/hid_device_manager.cc

@@ -143,7 +143,7 @@ bool HidDeviceManager::HasPermission(const Extension* extension,
 }
 
 void HidDeviceManager::UpdateDevices() {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  thread_checker_.CalledOnValidThread();
   HidService* hid_service = device::DeviceClient::Get()->GetHidService();
   DCHECK(hid_service);