Draw text drop shadows even when the text color is transparent

This matches Skia's behavior.

Change-Id: Ibf0a52611f5801cfa68169f66ab0ec06f256600f
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index 80f2081..45c97fa 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -779,6 +779,11 @@
     void resetDrawTextureTexCoords(float u1, float v1, float u2, float v2);
 
     /**
+     * Returns true if the specified paint will draw invisible text.
+     */
+    bool canSkipText(const SkPaint* paint) const;
+
+    /**
      * Binds the specified texture. The texture unit must have been selected
      * prior to calling this method.
      */