Calculate how much memory is used per account.

Prevent storing new data in AccountManager DB if too much storage is used.

Test: manual
Bug:273501008
Flag: EXEMPT security fix.

(cherry picked from commit 6b8138ca)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6264bccf0538dad70545773c296345fb6eaa4dc9)
Merged-In: I88a0fef8e2e7bc232768bd5f7aa3f4bf87cb1c2c
Change-Id: I88a0fef8e2e7bc232768bd5f7aa3f4bf87cb1c2c