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:cf1c6f266c883386e11d9a8dd883ea0a27277005)
Merged-In: I88a0fef8e2e7bc232768bd5f7aa3f4bf87cb1c2c
Change-Id: I88a0fef8e2e7bc232768bd5f7aa3f4bf87cb1c2c