[chromecast] Default BluetoothAdapterCast::powered_ = true

This is needed for Web Bluetooth to work on Chromecast.

Also, fix unrelated build error.

BUG=827672

Bug: b/75967216
Test: device_unittests, test page.
Change-Id: I216e544175a5729f81271abc9f64ae3509b94735
Reviewed-on: https://chromium-review.googlesource.com/1008876Reviewed-by: Stephen Lanham <slan@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Bailey Forrest <bcf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550010}

device/bluetooth/cast/bluetooth_adapter_cast.h

@@ -192,7 +192,7 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothAdapterCast
   chromecast::bluetooth::GattClientManager* const gatt_client_manager_;
   chromecast::bluetooth::LeScanManager* const le_scan_manager_;
 
-  bool powered_ = false;
+  bool powered_ = true;
   bool initialized_ = false;
 
   std::string name_;

device/bluetooth/test/bluetooth_test_cast.cc

@@ -31,9 +31,9 @@ class BluetoothTestCast::FakeLeScanManager
   void SetScanEnable(bool enable, SetScanEnableCallback cb) override {
     std::move(cb).Run(true);
   }
-  void GetScanResults(
-      GetScanResultsCallback cb,
-      base::Optional<uint16_t> service_uuid = base::nullopt) override {}
+  void GetScanResults(GetScanResultsCallback cb,
+                      base::Optional<chromecast::bluetooth::ScanFilter>
+                          scan_filter = base::nullopt) override {}
   void ClearScanResults() override {}
 
   Observer* observer() {