bluetooth: Perform an LE scan only

There isn't much support from platforms and devices for GATT over BR/EDR so
to avoid confusing users and wasting power, perform a LE scan only.

BUG=643625

Review-Url: https://codereview.chromium.org/2339033003
Cr-Commit-Position: refs/heads/master@{#418792}

content/browser/bluetooth/bluetooth_device_chooser_controller.cc

@@ -148,8 +148,12 @@ std::unique_ptr<device::BluetoothDiscoveryFilter> ComputeScanFilter(
       services.insert(service.value());
     }
   }
+  // There isn't much support for GATT over BR/EDR from neither platforms nor
+  // devices so performing a Dual scan will find devices that the API is not
+  // able to interact with. To avoid wasting power and confusing users with
+  // devices they are not able to interact with, we only perform an LE Scan.
   auto discovery_filter = base::MakeUnique<device::BluetoothDiscoveryFilter>(
-      device::BLUETOOTH_TRANSPORT_DUAL);
+      device::BLUETOOTH_TRANSPORT_LE);
   for (const BluetoothUUID& service : services) {
     discovery_filter->AddUUID(service);
   }

third_party/WebKit/Source/modules/bluetooth/README.md

@@ -5,6 +5,14 @@ Web Bluetooth
 
 [WB]: https://webbluetoothcg.github.io/web-bluetooth/
 
+Scanning
+--------------------------------------------------------------------------------
+There isn't much support for GATT over BR/EDR from neither platforms nor
+devices so performing a Dual scan will find devices that the API is not
+able to interact with. To avoid wasting power and confusing users with
+devices they are not able to interact with, navigator.bluetooth.requestDevice
+performs an LE-only Scan.
+
 Testing
 --------------------------------------------------------------------------------