Implement chrome.extension.connectExternal and fix various API inconsistencies.

chrome/test/data/extensions/good/Extensions/bjafgdebaacbbbecmhlhpofkepfkgcpa/1.0/toolstrip.html

 <script>
 window.onload = function() {
   chrome.extension.onConnect.addListener(function(port) {
     console.log('onConnect');
     port.onMessage.addListener(function(msg) {
       console.log('got message');
       if (msg.testPostMessageFromTab) {
         port.postMessage({success: true, portName: port.name});
         console.log('sent success');
       }
       // Ignore other messages since they are from us.
     });
   });
+  chrome.extension.onConnectExternal.addListener(function(port) {
+    port.onMessage.addListener(function(msg) {
+      if (msg.testConnectExternal) {
+        port.postMessage({success: true, senderId: port.sender.id});
+      }
+    });
+  });
 };
 
 // Tests that postMessage to the tab and its response works.
 function testPostMessage() {
   chrome.tabs.getSelected(null, function(tab) {
     var port = chrome.tabs.connect(tab.id);
     console.log('connect to ' + tab.id);
     port.postMessage({testPostMessage: true});
     port.onMessage.addListener(function(msg) {
       window.domAutomationController.send(msg.success);
@@ skipping 47 matching lines @@
   chrome.tabs.getSelected(null, function(tab) {
     var port = chrome.tabs.connect(tab.id);
     console.log('connect to ' + tab.id);
     port.postMessage({testDisconnectOnClose: true});
     port.onDisconnect.addListener(function() {
       window.domAutomationController.send(true);
     });
   });
 }
 </script>