Correctly implement the CLEAR xfermode.

The previous implementation was using glBlendFunc with the parameters
GL_ZERO/GL_ZERO which doesn't work for text, paths and other alpha
sources (anti-aliasing.) The correct implementation is GL_ZERO/
GL_ONE_MINUS_SRC_ALPHA.

Change-Id: I4cca65e57b6a37bbf5a41d382cb0648ee8e11e79
diff --git a/tests/HwAccelerationTest/AndroidManifest.xml b/tests/HwAccelerationTest/AndroidManifest.xml
index 35f2b9b..01d30eb 100644
--- a/tests/HwAccelerationTest/AndroidManifest.xml
+++ b/tests/HwAccelerationTest/AndroidManifest.xml
@@ -30,6 +30,15 @@
         android:hardwareAccelerated="true">
 
         <activity
+                android:name="ClearActivity"
+                android:label="_Clear">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+
+        <activity
                 android:name="TextureViewActivity"
                 android:label="_TextureView">
             <intent-filter>