Add accessibility text contrast setting

b/14624452

Adds a feature which draws all text (in the HW accelerated standard
path) in a high contrast mode. Text is drawn at full alpha, and either
white or black (depending on its original color) with a starkly
contrasted outline beneath it.

Change-Id: I943f624b6367de35367cced3b2a8298f2bc62377
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 2687bcc..1a0aadf 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -3675,6 +3675,14 @@
         public static final String ACCESSIBILITY_SPEAK_PASSWORD = "speak_password";
 
         /**
+         * Whether to draw text with high contrast while in accessibility mode.
+         *
+         * @hide
+         */
+        public static final String ACCESSIBILITY_HIGH_TEXT_CONTRAST_ENABLED =
+                "high_text_contrast_enabled";
+
+        /**
          * If injection of accessibility enhancing JavaScript screen-reader
          * is enabled.
          * <p>
@@ -4641,6 +4649,7 @@
             TOUCH_EXPLORATION_ENABLED,
             ACCESSIBILITY_ENABLED,
             ACCESSIBILITY_SPEAK_PASSWORD,
+            ACCESSIBILITY_HIGH_TEXT_CONTRAST_ENABLED,
             ACCESSIBILITY_CAPTIONING_ENABLED,
             ACCESSIBILITY_CAPTIONING_LOCALE,
             ACCESSIBILITY_CAPTIONING_BACKGROUND_COLOR,