Add help url for gestures settings.

Override getHelpResource() in GestureSettings and added corresponding
resource string for the help url.

Bug: 29792538
Change-Id: I2f2d93fc25b63266504bd13b954fefa5692e9ddf

res/values/strings.xml

@@ -5621,6 +5621,8 @@
     <string name="help_url_remote_display" translatable="false"></string>
     <!-- Help URL, Fingerprint [DO NOT TRANSLATE] -->
     <string name="help_url_fingerprint" translatable="false"></string>
+    <!-- Help URL, Gesture settings -->
+    <string name="help_url_gestures" translatable="false"></string>
 
     <!-- User account title [CHAR LIMIT=30] -->
     <string name="user_account_title">Account for content</string>

src/com/android/settings/gestures/GestureSettings.java

@@ -109,6 +109,11 @@ public class GestureSettings extends SettingsPreferenceFragment implements
         return true;
     }
 
+    @Override
+    protected int getHelpResource() {
+        return R.string.help_url_gestures;
+    }
+
     @Override
     protected int getMetricsCategory() {
         return MetricsEvent.SETTINGS_GESTURES;