Fix CollapsingToolbarBaseFragment crash on R.

The view with R.id.content_parent is a LinearLayout in the R layout
file, and will cause a ClassCastException on R.

Bug: 182960931
Bug: 183757373
Test: presubmit
Change-Id: I15bf8f14ac1e6b0986b040e25a2b5f57735b62a8