IndexedDB: Move content/renderer/indexed_db/ to Blink

Also in this CL:
- Add a :mojom_modules target to allow mojom files in this group
  to link against symbols that only exist in the modules layer.
- Rename indexed*db_struct_traits* to _mojom_traits*.

Bug: 717812
Change-Id: I85fa493b345bb6ab955316fe1725e4794ed4c99b
Reviewed-on: https://chromium-review.googlesource.com/c/1265900
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602911}
84 files changed