Stop providing Physical Web metadata after Bluetooth is disabled

ios/chrome/common/physical_web/physical_web_scanner.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/common/physical_web/physical_web_scanner.h"
 
 #import <CoreBluetooth/CoreBluetooth.h>
 
 #include <string>
 #include <vector>
@@ skipping 145 matching lines @@
   }
   [pendingRequests_ removeAllObjects];
   if (!pendingStart_ && [self bluetoothEnabled]) {
     [self reallyStop];
   }
   pendingStart_ = NO;
   started_ = NO;
 }
 
 - (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;
     // Sorts in ascending order.
     if ([device1 rank] > [device2 rank]) {
       return NSOrderedDescending;
     }
     if ([device1 rank] < [device2 rank]) {
       return NSOrderedAscending;
     }
     return NSOrderedSame;
@@ skipping 307 matching lines @@
         [strongSelf.get()->devices_ addObject:device];
         [strongSelf.get()->delegate_ scannerUpdatedDevices:weakSelf];
         [strongSelf.get()->finalUrls_ addObject:[device url]];
       }
     }
     [strongSelf.get()->pendingRequests_ removeObject:strongRequest];
   }];
 }
 
 @end