Add a preview image to the color mode preference.

For high-color displays, it's desirable to have a preview of the
impact the user's color preference will have on images.  This commit
adds that functionality to ColorModePreferenceFragment by extending
RadioButtonPickerFragment to support static content.

The image used here is a placeholder pending UX.

Bug: 73670362
Test: Added a test verifying that the preview is added correctly.
Change-Id: Id54316bbef6a22291a8e8acbda5fcb2839b88c23

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

@@ -16,10 +16,12 @@ package com.android.settings.display;
 import android.content.Context;
 import android.graphics.drawable.Drawable;
 import android.support.annotation.VisibleForTesting;
+import android.support.v7.preference.PreferenceScreen;
 
 import com.android.internal.app.ColorDisplayController;
 import com.android.internal.logging.nano.MetricsProto;
 
+import com.android.settings.applications.LayoutPreference;
 import com.android.settings.R;
 import com.android.settings.widget.RadioButtonPickerFragment;
 import com.android.settingslib.widget.CandidateInfo;
@@ -50,6 +52,19 @@ public class ColorModePreferenceFragment extends RadioButtonPickerFragment {
         return R.xml.color_mode_settings;
     }
 
+    @VisibleForTesting
+    void configureAndInstallPreview(LayoutPreference preview, PreferenceScreen screen) {
+        preview.setSelectable(false);
+        screen.addPreference(preview);
+    }
+
+    @Override
+    protected void addStaticPreferences(PreferenceScreen screen) {
+        final LayoutPreference preview = new LayoutPreference(screen.getContext(),
+                R.layout.color_mode_preview);
+        configureAndInstallPreview(preview, screen);
+    }
+
     @Override
     protected List<? extends CandidateInfo> getCandidates() {
         Context c = getContext();

src/com/android/settings/widget/RadioButtonPickerFragment.java

@@ -101,6 +101,13 @@ public abstract class RadioButtonPickerFragment extends InstrumentedPreferenceFr
         return false;
     }
 
+    /**
+     * Populate any static preferences, independent of the radio buttons.
+     * These might be used to provide extra information about the choices.
+     **/
+    protected void addStaticPreferences(PreferenceScreen screen) {
+    }
+
     protected CandidateInfo getCandidate(String key) {
         return mCandidates.get(key);
     }
@@ -134,6 +141,7 @@ public abstract class RadioButtonPickerFragment extends InstrumentedPreferenceFr
         final String systemDefaultKey = getSystemDefaultKey();
         final PreferenceScreen screen = getPreferenceScreen();
         screen.removeAll();
+        addStaticPreferences(screen);
 
         final int customLayoutResId = getRadioButtonPreferenceCustomLayoutResId();
         if (shouldShowItemNone()) {