[chromecast] BLE: Silently ignore unrecognized disconnenect events

- There may be other processes in the system which are
  connecting/disconnecting BLE devices.
- We may receive extra disconnect events

Bug: b/110965632
Test: Does not log if called with unrecognized device.
Change-Id: I3059435ea5df6919e12a87852c27e716a0f106b5
Reviewed-on: https://chromium-review.googlesource.com/1119657
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Bailey Forrest <bcf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574436}

chromecast/device/bluetooth/le/gatt_client_manager_impl.cc

@@ -117,7 +117,11 @@ void GattClientManagerImpl::OnConnectChanged(
     bool connected) {
   MAKE_SURE_IO_THREAD(OnConnectChanged, addr, status, connected);
   auto it = addr_to_device_.find(addr);
-  CHECK_DEVICE_EXISTS_IT(it);
+
+  // Silently ignore devices we aren't keeping track of.
+  if (it == addr_to_device_.end()) {
+    return;
+  }
 
   it->second->SetConnected(connected);
   if (connected) {