Move mFragmentContainerViewId out of ChromePdfViewerFragment

This is to resolve crash/cb46ba85a0d6f523
Fragment class requires a public, no-arg constructor.
Move mFragmentContainerViewId out of ChromePdfViewerFragment so that the
constructor does not require an arg.

Bug: 363203688
Change-Id: Ic80222ff9b251b4d760b4c9cdf9d640061adf865
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5827212
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Shu Yang <shuyng@google.com>
Reviewed-by: Sirisha Kavuluru <skavuluru@google.com>
Cr-Commit-Position: refs/heads/main@{#1349985}