Add an API to manipulate the browser action badge.

chrome/test/data/extensions/samples/make_page_red/background.html

Index: chrome/test/data/extensions/samples/make_page_red/background.html
diff --git a/chrome/test/data/extensions/samples/make_page_red/background.html b/chrome/test/data/extensions/samples/make_page_red/background.html
index 084359575d6d02c3ddacd7b765622683851cb02b..30631d23222de858687dfc6bb05fec2ffe9bd928 100755
--- a/chrome/test/data/extensions/samples/make_page_red/background.html
+++ b/chrome/test/data/extensions/samples/make_page_red/background.html
@@ -5,6 +5,14 @@
   chrome.browserAction.onClicked.addListener(function(windowId) {
     chrome.tabs.executeScript(null, {code:"document.body.bgColor='red'"});
   });
+
+  chrome.browserAction.setBadgeBackgroundColor([100, 0, 200, 0]);
+
+  var i = 0;
+  window.setInterval(function() {
+    chrome.browserAction.setBadgeText(String(i));
+    i++;
+  }, 10);
 </script>
 </head>
 </html>