cmsdk: Ensure CMHW feature constants aren't optimized out

* The preferences constraints system uses reflection to look up
   fields via strings, we need to ensure they are not optimized
   out by Proguard. Alternatively we can manually enumerate them,
   but it's yet another list of constants to maintain. We should
   have used a proper enumeration to begin with, but so it goes.
 * The @VisibleForTesting annotation is honored by the platform for
   ensuring that Proguard doesn't stomp fields. The support library
   has an @Keep annotation, but it's only supported by Gradle. If
   it becomes supported by the platform in the future, switch to
   it instead.
 * Also add tests for all of this.

Change-Id: I9f324e003e2a9de5604085b978d5f95bdd098d32

sdk/src/java/cyanogenmod/hardware/CMHardwareManager.java

@@ -22,6 +22,8 @@ import android.os.ServiceManager;
 import android.util.Log;
 import android.util.Range;
 
+import com.android.internal.annotations.VisibleForTesting;
+
 import cyanogenmod.app.CMContextConstants;
 import cyanogenmod.hardware.HSIC;
 
@@ -46,103 +48,127 @@ public final class CMHardwareManager {
     private static ICMHardwareService sService;
 
     private Context mContext;
+
+    /* The VisibleForTesting annotation is to ensure Proguard doesn't remove these
+     * fields, as they might be used via reflection. When the @Keep annotation in
+     * the support library is properly handled in the platform, we should change this.
+     */
+
     /**
      * Adaptive backlight support (this refers to technologies like NVIDIA SmartDimmer,
      * QCOM CABL or Samsung CABC)
      */
+    @VisibleForTesting
     public static final int FEATURE_ADAPTIVE_BACKLIGHT = 0x1;
 
     /**
      * Color enhancement support
      */
+    @VisibleForTesting
     public static final int FEATURE_COLOR_ENHANCEMENT = 0x2;
 
     /**
      * Display RGB color calibration
      */
+    @VisibleForTesting
     public static final int FEATURE_DISPLAY_COLOR_CALIBRATION = 0x4;
 
     /**
      * Display gamma calibration
      */
+    @VisibleForTesting
     public static final int FEATURE_DISPLAY_GAMMA_CALIBRATION = 0x8;
 
     /**
      * High touch sensitivity for touch panels
      */
+    @VisibleForTesting
     public static final int FEATURE_HIGH_TOUCH_SENSITIVITY = 0x10;
 
     /**
      * Hardware navigation key disablement
      */
+    @VisibleForTesting
     public static final int FEATURE_KEY_DISABLE = 0x20;
 
     /**
      * Long term orbits (LTO)
      */
+    @VisibleForTesting
     public static final int FEATURE_LONG_TERM_ORBITS = 0x40;
 
     /**
      * Serial number other than ro.serialno
      */
+    @VisibleForTesting
     public static final int FEATURE_SERIAL_NUMBER = 0x80;
 
     /**
      * Increased display readability in bright light
      */
+    @VisibleForTesting
     public static final int FEATURE_SUNLIGHT_ENHANCEMENT = 0x100;
 
     /**
      * Double-tap the touch panel to wake up the device
      */
+    @VisibleForTesting
     public static final int FEATURE_TAP_TO_WAKE = 0x200;
 
     /**
      * Variable vibrator intensity
      */
+    @VisibleForTesting
     public static final int FEATURE_VIBRATOR = 0x400;
 
     /**
      * Touchscreen hovering
      */
+    @VisibleForTesting
     public static final int FEATURE_TOUCH_HOVERING = 0x800;
 
     /**
      * Auto contrast
      */
+    @VisibleForTesting
     public static final int FEATURE_AUTO_CONTRAST = 0x1000;
 
     /**
      * Display modes
      */
+    @VisibleForTesting
     public static final int FEATURE_DISPLAY_MODES = 0x2000;
 
     /**
      * Persistent storage
      */
+    @VisibleForTesting
     public static final int FEATURE_PERSISTENT_STORAGE = 0x4000;
 
     /**
      * Thermal change monitor
      */
+    @VisibleForTesting
     public static final int FEATURE_THERMAL_MONITOR = 0x8000;
 
     /**
      * Unique device ID
      */
+    @VisibleForTesting
     public static final int FEATURE_UNIQUE_DEVICE_ID = 0x10000;
 
     /**
      * Color balance
      */
+    @VisibleForTesting
     public static final int FEATURE_COLOR_BALANCE = 0x20000;
 
     /**
      * HSIC picture adjustment
      */
+    @VisibleForTesting
     public static final int FEATURE_PICTURE_ADJUSTMENT = 0x40000;
 
-
     private static final List<Integer> BOOLEAN_FEATURES = Arrays.asList(
         FEATURE_ADAPTIVE_BACKLIGHT,
         FEATURE_COLOR_ENHANCEMENT,
@@ -241,7 +267,7 @@ public final class CMHardwareManager {
                 return isSupported((int) f.get(null));
             }
         } catch (NoSuchFieldException | IllegalAccessException e) {
-            // ignore
+            Log.d(TAG, e.getMessage(), e);
         }
 
         return false;