[Android] Fix help context string for SyncAndServicesPreferences

This CL changes help context string introduced by
https://crrev.com/c/1299133 for "?" button in "Sync and Google services"
settings page.

Bug: 885333
Change-Id: Ibe24f7f85ad4080dea0eae55efeb7810cb026430
Reviewed-on: https://chromium-review.googlesource.com/c/1304555Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603523}

chrome/android/java/res/values/values.xml

@@ -57,7 +57,7 @@
     <string name="help_context_sad_tab">mobile_awsnap</string>
     <string name="help_context_clear_browsing_data">clear_browsing_data</string>
     <string name="help_context_change_sync_passphrase">change_sync_passphrase</string>
-    <string name="help_context_sync_and_services">sync_and_services</string>
+    <string name="help_context_sync_and_services">syncgoogleservices</string>
     <!-- TODO(peconn): Add help section. -->
     <!-- <string name="help_context_suggestions">mobile_content_suggestions</string> -->