Catch reentrancy while executing postponed transactions.

Bug 35349893

While executing postponed transactions, it was possible for
Fragments to call commitNow() or executePendingTransactions()
and therefore causing disallowed reentrancy.

This CL now prevents reentrancy while executing postponed
transactions.

Test: ran fragment/ tests
Change-Id: I90935fbae1cf0bcb90f041803f97d7dfa6a70d56
2 files changed