cmsdk: Add constraints support for CMHardware features

* This patch will make it easy to hide preferences based on the
   lack of a CMHardware feature. In the preference, specify this:

     cm:requiresFeature="cmhardware:FEATURE_KEY_DISABLE"

   ..and the preference will magically be removed if the feature
   is not supported.

Change-Id: I51699df7b39bb38b9ea69c93ade658736f89b988

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

@@ -27,6 +27,7 @@ import cyanogenmod.hardware.HSIC;
 
 import java.io.UnsupportedEncodingException;
 import java.lang.IllegalArgumentException;
+import java.lang.reflect.Field;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.List;
@@ -225,6 +226,26 @@ public final class CMHardwareManager {
         return feature == (getSupportedFeatures() & feature);
     }
 
+    /**
+     * String version for preference constraints
+     *
+     * @hide
+     */
+    public boolean isSupported(String feature) {
+        if (!feature.startsWith("FEATURE_")) {
+            return false;
+        }
+        try {
+            Field f = getClass().getField(feature);
+            if (f != null) {
+                return isSupported((int) f.get(null));
+            }
+        } catch (NoSuchFieldException | IllegalAccessException e) {
+            // ignore
+        }
+
+        return false;
+    }
     /**
      * Determine if the given feature is enabled or disabled.
      *

sdk/src/java/cyanogenmod/preference/ConstraintsHelper.java

@@ -29,6 +29,7 @@ import android.text.TextUtils;
 import android.util.AttributeSet;
 import android.util.TypedValue;
 
+import cyanogenmod.hardware.CMHardwareManager;
 import cyanogenmod.platform.R;
 
 
@@ -115,8 +116,15 @@ public class ConstraintsHelper {
 
             // Check if a system feature is available
             String rFeature = a.getString(R.styleable.cm_SelfRemovingPreference_requiresFeature);
-            if (rFeature != null && !hasSystemFeature(mContext, rFeature)) {
-                return false;
+            if (rFeature != null) {
+                if (rFeature.startsWith("cmhardware:")) {
+                    if (!CMHardwareManager.getInstance(mContext).isSupported(
+                            rFeature.substring("cmhardware:".length()))) {
+                        return false;
+                    }
+                } else if (!hasSystemFeature(mContext, rFeature)) {
+                    return false;
+                }
             }
 
             // Check a boolean system property