Grey out settings icon when it is in disabled state

If engine is not active, its settings icon is disabled in
Settings > Language & input > Text-to-speech output screen.
Currently, settings icons for all TTS engines are shown at
the same opacity. This fix dims settings icons of not-selected
engines.
Make sure that more than one TTS engine are installed on the
target, for e.g., Google Text-to-speech Engine and Classic
Text To Speech Engine (SVOX Classic TTS).

Additionally, since setAlpha() is used in multiple places within
Settings package, moved DISABLED_ALPHA declaration to Utils.java
in order to have single point of reference.

Change-Id: Ifa7de79814a2f4a4aa021cd8621cbfab41655680
Signed-off-by: Shuhrat Dehkanov <uzbmaster@gmail.com>

src/com/android/settings/inputmethod/CheckBoxAndSettingsPreference.java

@@ -18,6 +18,7 @@ package com.android.settings.inputmethod;
 
 import com.android.settings.R;
 import com.android.settings.SettingsPreferenceFragment;
+import com.android.settings.Utils;
 
 import android.content.Context;
 import android.content.Intent;
@@ -29,7 +30,6 @@ import android.widget.ImageView;
 import android.widget.TextView;
 
 public class CheckBoxAndSettingsPreference extends CheckBoxPreference {
-    private static final float DISABLED_ALPHA = 0.4f;
 
     private SettingsPreferenceFragment mFragment;
     private TextView mTitleText;
@@ -103,7 +103,7 @@ public class CheckBoxAndSettingsPreference extends CheckBoxPreference {
                 mSettingsButton.setClickable(checked);
                 mSettingsButton.setFocusable(checked);
                 if (!checked) {
-                    mSettingsButton.setAlpha(DISABLED_ALPHA);
+                    mSettingsButton.setAlpha(Utils.DISABLED_ALPHA);
                 }
             }
         }