WebBluetooth Scanning - DCHECK if ExecutionContext is null.

Bug: 897312
Change-Id: I3f156092b1d5687fce06ef05b2f6cf4db1d9ba32
Reviewed-on: https://chromium-review.googlesource.com/c/1388809
Commit-Queue: Doug Turner <dougt@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619741}

third_party/blink/renderer/modules/bluetooth/bluetooth.cc

@@ -246,6 +246,7 @@ ScriptPromise Bluetooth::requestLEScan(ScriptState* script_state,
                                        const BluetoothLEScanOptions* options,
                                        ExceptionState& exception_state) {
   ExecutionContext* context = ExecutionContext::From(script_state);
+  DCHECK(context);
 
   // Remind developers when they are using Web Bluetooth on unsupported
   // platforms.
@@ -303,9 +304,11 @@ ScriptPromise Bluetooth::requestLEScan(ScriptState* script_state,
 }
 
 void Bluetooth::ScanEvent(mojom::blink::WebBluetoothScanResultPtr result) {
-  ExecutionContext* content = ContextLifecycleObserver::GetExecutionContext();
+  ExecutionContext* context = ContextLifecycleObserver::GetExecutionContext();
+  DCHECK(context);
+
   BluetoothDevice* bluetooth_device =
-      GetBluetoothDeviceRepresentingDevice(std::move(result->device), content);
+      GetBluetoothDeviceRepresentingDevice(std::move(result->device), context);
 
   HeapVector<blink::StringOrUnsignedLong> uuids;
   for (const String& uuid : result->uuids) {