Add get_api() function

src/android/mod.rs

@@ -265,6 +265,10 @@ impl Window {
     pub fn platform_display(&self) -> *mut libc::c_void {
         self.display as *mut libc::c_void
     }
+
+    pub fn get_api(&self) -> ::Api {
+        ::Api::OpenGlEs
+    }
 }
 
 #[unsafe_destructor]