Restrict app sandbox's CSP to disallow loading web content in them.

chrome/test/data/extensions/api_test/sandboxed_pages_csp/sandboxed.html

+This page should be sandboxed.
+
+<script>
+// We're not served with the extension default CSP, we can use inline script.
+
+var loadFrameExpectResponse = function(iframe, url) {
+  var identifier = +new Date;
+  return new Promise(function(resolve, reject) {
+    window.addEventListener('message', function(e) {
+      var data = JSON.parse(e.data);
+      if (data[0] == 'pong' && data[1] == identifier) {

[Devlin, 2016/12/22 17:04:32]

all these pings and pongs are getting hard to keep track of.  Could we instead
do something like 'sandboxed frame', etc?

[lazyboy, 2016/12/22 22:57:06]

Changed to sandboxed frame msg <-> local/remote frame msg

+        resolve();
+      } else {
+        reject();
+      }
+    });
+    iframe.onerror = reject;
+    iframe.onload = function() {
+      iframe.contentWindow.postMessage(
+          JSON.stringify(['ping', identifier]), '*');
+    };
+    iframe.src = url;
+  });
+};
+
+var runTestAndRespond = function(localUrl, remoteUrl) {
+  var iframe = document.createElement('iframe');
+  var sendResponse = function(msg) {
+    var mainWindow = window.opener || window.top;
+    mainWindow.postMessage(msg, '*');
+  };
+
+  // First load local resource in |iframe|, expect the local frame to respond.
+  loadFrameExpectResponse(iframe, localUrl).then(function() {
+    // Then try to load remote resource on the same iframe element. Since the
+    // remote resource will fail to load, expect the local frame to respond

[Devlin, 2016/12/22 17:04:32]

I don't quite follow.  So in trying to commit an invalid url, we reload the
current url?

[lazyboy, 2016/12/22 22:57:06]

We keep the current url and resource as is, but iframe.onload fires.

+    // again.
+    return loadFrameExpectResponse(iframe, remoteUrl);
+  }).then(function() {
+    sendResponse('succeeded');
+  }).catch(function(err) {
+    sendResponse('failed');
+  });
+  document.body.appendChild(iframe);
+};
+
+onmessage = function(e) {
+  var command = JSON.parse(e.data);
+  if (command[0] == 'load') {
+    var localUrl = command[1];
+    var remoteUrl = command[2];
+    runTestAndRespond(localUrl, remoteUrl);
+  }
+};
+
+</script>