Makes loading test resources load the first supported scale factor

This is necessary as we don't always load 1x resources. In particular
when I run views_example_exe with --force-device-scale-factor=2 then
1x isn't loaded.

BUG=none
TEST=none
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/564473002

Cr-Commit-Position: refs/heads/master@{#294196}

ui/base/resource/resource_bundle.cc

@@ -321,8 +321,10 @@ std::string ResourceBundle::LoadLocaleResources(
 
 void ResourceBundle::LoadTestResources(const base::FilePath& path,
                                        const base::FilePath& locale_path) {
+  DCHECK(!ui::GetSupportedScaleFactors().empty());
+  const ScaleFactor scale_factor(ui::GetSupportedScaleFactors()[0]);
   // Use the given resource pak for both common and localized resources.
-  scoped_ptr<DataPack> data_pack(new DataPack(SCALE_FACTOR_100P));
+  scoped_ptr<DataPack> data_pack(new DataPack(scale_factor));
   if (!path.empty() && data_pack->LoadFromPath(path))
     AddDataPack(data_pack.release());