Use polling instead of XHR for callbacks from Java to JavaScript when device has a proxy set.

framework/assets/js/phonegap.js.base

@@ -238,7 +238,14 @@ PhoneGap.onDeviceReady = new PhoneGap.Channel('onDeviceReady');
 PhoneGap.Channel.join(function() {
 
     // Start listening for XHR callbacks
-    PhoneGap.JSCallback();
+    setTimeout(function() {
+            if (CallbackServer.usePolling()) {
+                PhoneGap.JSCallbackPolling();
+            }
+            else {
+                PhoneGap.JSCallback();
+            }
+        }, 1);
 
     // Run PhoneGap constructors
     PhoneGap.onPhoneGapInit.fire();
@@ -603,6 +610,37 @@ PhoneGap.JSCallback = function() {
     xmlhttp.send();
 };
 
+/**
+ * The polling period to use with JSCallbackPolling.
+ * This can be changed by the application.  The default is 50ms.
+ */
+PhoneGap.JSCallbackPollingPeriod = 50;
+
+/**
+ * This is only for Android.
+ *
+ * Internal function that uses polling to call into PhoneGap Java code and retrieve 
+ * any JavaScript code that needs to be run.  This is used for callbacks from
+ * Java to JavaScript.
+ */
+PhoneGap.JSCallbackPolling = function() {
+    var msg = CallbackServer.getJavascript();
+    if (msg) {
+        setTimeout(function() {
+            try {
+                var t = eval(""+msg);
+            }
+            catch (e) {
+                console.log("JSCallbackPolling Error: "+e);
+            }
+        }, 1);
+        setTimeout(PhoneGap.JSCallbackPolling, 1);
+    }
+    else {
+        setTimeout(PhoneGap.JSCallbackPolling, PhoneGap.JSCallbackPollingPeriod);
+    }
+};
+
 /**
  * Create a UUID
  *