Refactor SyncBackendHost

Split SyncBackendHost into SyncBackendHost, SyncBackendHostImpl and
SyncBackendHostCore.

The SyncBackendHost class is now a pure virtual interface.  It is the
contains the interface exposed to the ProfileSyncService.

The SyncBackendHostImpl class implements the functionality of the
SyncBackendHost.  It contains most of the code that used to reside in
SyncBackendHost.

The SyncBackendHostCore is the old SyncBackendHost::Core under a new
name.  It's been moved out of the SyncBackendHost's .cc file and into
its own, publicly declared class.  This will hopefully enable better
testing in the future.

This is a pure refactoring change.  It should have no impact on program
behavior.

BUG=312999

Review URL: https://codereview.chromium.org/61183003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233533 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233533
Link LinuxInputMethodContextFactory instead of skipping a call to its SetInstance().

This is a better solution for long term for http://crrev.com/44453003 .

BUG=133476
TEST=none

Review URL: https://codereview.chromium.org/54463009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233534 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233534
Disable ExternallyConnectableMessagingTest.WebConnectableWithEmptyTlsChannelIdAndClosedBackgroundPage on Linux official bot.

This test fails intermittently on official Linux bot with TIMED OUT error. See http://crbug.com/315264 for more details.
 

BUG=315264

Review URL: https://codereview.chromium.org/61063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233535 0039d316-1c4b-4281-b951-d872f2087c98
Remove render_process_host_factory_ from SiteInstanceImpl.

This member has been unused and uninitialized since r204409,
but it looks like we forgot to actually remove the member.

BUG=NONE
TEST=trybots

Review URL: https://codereview.chromium.org/61163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233536 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233536