Add tests for chrome.fileSystem app API.

chrome/browser/extensions/api/file_system/file_system_api.h

Index: chrome/browser/extensions/api/file_system/file_system_api.h
diff --git a/chrome/browser/extensions/api/file_system/file_system_api.h b/chrome/browser/extensions/api/file_system/file_system_api.h
index 2acf23a4f1050edf8f01ba4eeee3f0743d278e1f..ff0e486ec9defe0bec65890dc47514257dbc0573 100644
--- a/chrome/browser/extensions/api/file_system/file_system_api.h
+++ b/chrome/browser/extensions/api/file_system/file_system_api.h
@@ -20,6 +20,12 @@ class FileSystemGetDisplayPathFunction : public SyncExtensionFunction {
 };
 
 class FileSystemPickerFunction : public AsyncExtensionFunction {
+ public:
+  // Allow picker UI to be skipped in testing.
+  static void SkipPickerAndAlwaysSelectPath(FilePath* path);
+  static void SkipPickerAndAlwaysCancel();
+  static void StopSkippingPicker();
+
  protected:
   class FilePicker;