Always reserve space for preference icons.

This aligns text on preferences on the same screen when some of them
don't have icons.

- Use a custom layout for
  preference
  EditPreference
  switch preference
  VolumeSeekPreference
  DialogPreferencei
  Restricted*Preference
  DropdownPreference

- Moved related style defs into a new file styles_preference.xml,
  because current styles file is too large to read.
- Switch <PreferenceScreen ...> to <Preference ...> for a bunch of
  regular preferences.
- Also removed some dead style.

Bug: 33430928
Test: runtest --path packages/apps/Settings/tests/app/src/com/android/settings/dashboard/PreferenceThemeTest.java

Change-Id: Ic9b75d3f133f2a83cd999297b8596253d4b10161

src/com/android/settings/display/ScreenZoomPreference.java

@@ -16,23 +16,23 @@
 
 package com.android.settings.display;
 
-import com.android.settingslib.display.DisplayDensityUtils;
-
 import android.content.Context;
 import android.support.v4.content.res.TypedArrayUtils;
-import android.support.v7.preference.PreferenceGroup;
+import android.support.v7.preference.Preference;
 import android.text.TextUtils;
 import android.util.AttributeSet;
 
+import com.android.settingslib.display.DisplayDensityUtils;
+
 /**
  * Preference for changing the density of the display on which the preference
  * is visible.
  */
-public class ScreenZoomPreference extends PreferenceGroup {
+public class ScreenZoomPreference extends Preference {
     public ScreenZoomPreference(Context context, AttributeSet attrs) {
         super(context, attrs, TypedArrayUtils.getAttr(context,
-                android.support.v7.preference.R.attr.preferenceScreenStyle,
-                android.R.attr.preferenceScreenStyle));
+                android.support.v7.preference.R.attr.preferenceStyle,
+                android.R.attr.preferenceStyle));
 
         if (TextUtils.isEmpty(getFragment())) {
             setFragment("com.android.settings.display.ScreenZoomSettings");
@@ -49,9 +49,4 @@ public class ScreenZoomPreference extends PreferenceGroup {
             setSummary(entries[currentIndex]);
         }
     }
-
-    @Override
-    protected boolean isOnSameScreenAsChildren() {
-        return false;
-    }
 }