fix: update to work with Karma 0.11

Since Karma executes immediately, we don't have all the browsers in advance, the reporter has to listen on browser_start instead.

This re-introduces b744d6f but in a back-compatible way.

lib/reporter.js

@@ -64,10 +64,18 @@ var CoverageReporter = function(rootConfig, helper, logger) {
   }
 
   this.onRunStart = function(browsers) {
-    collectors = {};
-    browsers.forEach(function(browser) {
-      collectors[browser.id] = new istanbul.Collector();
-    });
+    collectors = Object.create(null);
+
+    // TODO(vojta): remove once we don't care about Karma 0.10
+    if (browsers) {
+      browsers.forEach(function(browser) {
+        collectors[browser.id] = new istanbul.Collector();
+      });
+    }
+  };
+
+  this.onBrowserStart = function(browser) {
+    collectors[browser.id] = new istanbul.Collector();
   };
 
   this.onBrowserComplete = function(browser, result) {

test/reporter.spec.coffee

@@ -120,7 +120,8 @@ describe 'reporter', ->
       fakeOpera = makeBrowser 'bbb', 'Opera/9.80 Mac OS X Version/12.00', browsers, emitter
       browsers.add fakeChrome
       browsers.add fakeOpera
-      reporter.onRunStart browsers
+      reporter.onRunStart()
+      browsers.forEach (b) -> reporter.onBrowserStart b
       mockFs.writeFile.reset()
       mockMkdir.reset()