scanning: Set scan request settings all at once

Instead of manually setting each scan setting in the StartScanRequest of
LorgnetteManagerClient::StartScan(), set them all at once using the
given ScanSettings proto. This will eliminate the need to manually set
additional settings that get added to the proto in the future.

Bug: None
Change-Id: I05f734c630beed8e9cfb9a7a5359c9441d5f0502
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2432310Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811353}

chromeos/dbus/lorgnette_manager_client.cc

@@ -74,10 +74,7 @@ class LorgnetteManagerClientImpl : public LorgnetteManagerClient {
                      progress_callback) override {
     lorgnette::StartScanRequest request;
     request.set_device_name(device_name);
-    request.mutable_settings()->set_color_mode(settings.color_mode());
-    request.mutable_settings()->set_resolution(settings.resolution());
-    lorgnette::DocumentSource source = settings.source();
-    request.mutable_settings()->set_allocated_source(&source);
+    *request.mutable_settings() = settings;
 
     dbus::MethodCall method_call(lorgnette::kManagerServiceInterface,
                                  lorgnette::kStartScanMethod);