Merge pull request #22637 from lightsofapollo/reland-webcomp-off

Bug 1038439 - Remove web components preference from Gaia. r=vingtetun
Bug 1050097 - [Camera] Add error handling while |videoStorage.addNamed| occurs error.
Bug 1042221 - [email/backend] v2.0 specific uplift of improved saving/shutdown behaviour. r=asuth,r=mcav,r=jrburke, a=blocking-b2g=2.0

This includes the following fixes:

Portions of Bug 921050 (background sending), primarily cleanup
cleanup portions authored by asuth, melded into mcav's background send logic, mcav did extra cleanup
r=asuth on the mcav bits, r=mcav on the asuth bits

Bug 1039007 - Do not invoke operation callbacks until after any associated saves have safely hit the disk.
patch by asuth, r=mcav

Bug 987931 - cronsync's self-close races an IndexedDB commit.
patch by asuth, portions by jrburke.  r=mcav, r=jrburke, r=asuth

This amalgamation prepared and tested by asuth.
Merge pull request #22810 from mpizza/Bug_1050097_v2.0

Bug 1050097 - [Camera] Add error handling while |videoStorage.addNamed| occurs error. r=diego.
Revert "Bug 1050097 - [Camera] Add error handling while |videoStorage.addNamed| occurs error."

This reverts commit 56a1bfe3fc03ab235a7aa6f2979c1cee95ca147b.
Merge pull request #22279 from asutherland/email-save-uplifts

Bug 1042221 - [email/backend] v2.0 specific uplift of improved saving/shutdown behaviour. r=mcav, r=jrburke, r=asuth, a=blocking-b2g=2.0