Move manifest_url_handler to //extensions
This moves extensions manifest URL handlers into //extensions
and renames the source files more appropriately to
"manifest_url_handlers"
Mechanical change, so all this noise is only header updates.
TBRs are for header changes only.
BUG=398671
TBR=derat@chromium.org for app_mode change
TBR=pkotwicz@chromium.org for themes change
TBR=msw@chromium.org for ui changes
Review URL: https://codereview.chromium.org/
651353002
Cr-Commit-Position: refs/heads/master@{#299598}