Move OnURLsDeleted from NTPSnippetsService to ContentSuggestionsService

Move OnURLsDeleted from NTPSnippetsService to ContentSuggestionsService

This CL makes ContentSuggestionsService an observer of HistoryService,
so that all providers can be notified about deleted URLs.
The call is redirected to ClearHistory().
NTPSnippetsService's HistoryService observer code is replaced with
the notification above.

BUG=643608
Review-Url: https://codereview.chromium.org/2292003002
Cr-Commit-Position: refs/heads/master@{#416518}
(cherry picked from commit 45941154e2a8e0766210a65d2c12bf40a2c95d9a)

Committed: https://chromium.googlesource.com/chromium/src/+/14ed9ad4d92994f05c83d15c2e21154c0dcbdab7

[Marc Treib, 2016-09-07 09:54:22]

Description was changed from

==========
Move OnURLsDeleted from NTPSnippetsService to ContentSuggestionsService

This CL makes ContentSuggestionsService an observer of HistoryService,
so that all providers can be notified about deleted URLs.
The call is redirected to ClearHistory().
NTPSnippetsService's HistoryService observer code is replaced with
the notification above.

BUG=643608

Review-Url: https://codereview.chromium.org/2292003002
Cr-Commit-Position: refs/heads/master@{#416518}
(cherry picked from commit 45941154e2a8e0766210a65d2c12bf40a2c95d9a)
==========

to

==========
Move OnURLsDeleted from NTPSnippetsService to ContentSuggestionsService

This CL makes ContentSuggestionsService an observer of HistoryService,
so that all providers can be notified about deleted URLs.
The call is redirected to ClearHistory().
NTPSnippetsService's HistoryService observer code is replaced with
the notification above.

BUG=643608

Review-Url: https://codereview.chromium.org/2292003002
Cr-Commit-Position: refs/heads/master@{#416518}
(cherry picked from commit 45941154e2a8e0766210a65d2c12bf40a2c95d9a)

Committed:
https://chromium.googlesource.com/chromium/src/+/14ed9ad4d92994f05c83d15c2e21...
==========

[Marc Treib, 2016-09-07 09:54:24]

Committed patchset #1 (id:1) manually as
14ed9ad4d92994f05c83d15c2e21154c0dcbdab7.