Tidy: Modernize MockFileSystemAccessPermission* destructors

Annotates destructor with "override"
- MockFileSystemAccessPermissionContext
- MockFileSystemAccessPermissionGrant

Bug: N/A
Change-Id: I0182c5040282b1e8da0ee0a2f91871fe68c592f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618368
Commit-Queue: Austin Sullivan <asully@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843372}

content/browser/file_system_access/mock_file_system_access_permission_context.h

@@ -15,7 +15,7 @@ class MockFileSystemAccessPermissionContext
     : public FileSystemAccessPermissionContext {
  public:
   MockFileSystemAccessPermissionContext();
-  ~MockFileSystemAccessPermissionContext();
+  ~MockFileSystemAccessPermissionContext() override;
 
   MOCK_METHOD4(GetReadPermissionGrant,
                scoped_refptr<FileSystemAccessPermissionGrant>(

content/browser/file_system_access/mock_file_system_access_permission_grant.h

@@ -30,7 +30,7 @@ class MockFileSystemAccessPermissionGrant
   using FileSystemAccessPermissionGrant::NotifyPermissionStatusChanged;
 
  protected:
-  ~MockFileSystemAccessPermissionGrant();
+  ~MockFileSystemAccessPermissionGrant() override;
 };
 
 }  // namespace content