Stop providing Physical Web metadata after Bluetooth is disabled

ios/chrome/common/physical_web/physical_web_scanner.mm

Index: ios/chrome/common/physical_web/physical_web_scanner.mm
diff --git a/ios/chrome/common/physical_web/physical_web_scanner.mm b/ios/chrome/common/physical_web/physical_web_scanner.mm
index d35a6689a3aa44caa3fe2e9b864945c8a3628aa6..f07a82ed53c1308f103d01d737cbc0c886330549 100644
--- a/ios/chrome/common/physical_web/physical_web_scanner.mm
+++ b/ios/chrome/common/physical_web/physical_web_scanner.mm
@@ -163,6 +163,9 @@ enum BeaconType {
 }
 
 - (NSArray*)devices {
+  if (![self bluetoothEnabled]) {
+    return [NSArray array];
+  }
   return [devices_ sortedArrayUsingComparator:^(id obj1, id obj2) {

[Olivier, 2016/11/17 09:04:36]

Should we clear devices_ ?

[mattreynolds, 2016/11/18 00:03:25]

When onLostDetectionEnabled_==NO, I think we shouldn't remove from devices_. The
scanner already has logic to handle changes to the Bluetooth state.

When onLostDetectionEnabled_==YES, the current behavior is to remove the devices
if they haven't been seen for kLostThresholdSeconds. But, the OnLost check
doesn't get run when Bluetooth is disabled, so they won't be removed until the
next time Bluetooth is enabled.

IMO it would be best to use the same logic to remove devices regardless of the
Bluetooth state. To allow the OnLost check to remove them, the repeating timer
needs to run while Bluetooth is disabled. I modified the timer so it stops
itself when there are no more nearby URLs.

     PhysicalWebDevice* device1 = obj1;
     PhysicalWebDevice* device2 = obj2;