libchromeos: Make XServerRunner emit x-started.

Make the XServerRunner class emit the x-started Upstart
signal and record the corresponding bootstat marker instead
of making clients do it themselves.

BUG=chromium:377301
TEST=manual: ran it and checked that bootstat marker is
     present
CQ-DEPEND=I087ecf5e873d6e61b2e97e798aa1b76b7976a80c

Change-Id: Ia5bf468cc4775ba1abfe59ef8caa0ca4ce783f63
Reviewed-on: https://chromium-review.googlesource.com/203290
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Daniel Erat <derat@chromium.org>
Commit-Queue: Daniel Erat <derat@chromium.org>
Tested-by: Daniel Erat <derat@chromium.org>
diff --git a/libchromeos.gypi b/libchromeos.gypi
index 0d9ff7d..3936405 100644
--- a/libchromeos.gypi
+++ b/libchromeos.gypi
@@ -66,7 +66,10 @@
       'target_name': 'libchromeos-cryptohome-<(libbase_ver)',
       'type': 'shared_library',
       'variables': {
-        'exported_deps': ['openssl'],
+        'exported_deps': [
+          'bootstat',
+          'openssl',
+        ],
         'deps': ['<@(exported_deps)'],
       },
       'cflags': [