fix(scope): log firing expressions in the watchLog

lib/core/scope.dart

@@ -439,6 +439,11 @@ class Scope implements Map {
 
         watcherCount = 0;
         scopeCount = 0;
+        var firedExpressions;
+        if (_ttl - _ttlLeft > 2) {
+          firedExpressions = <String>[];
+          watchLog.add(firedExpressions);
+        }
         assert((timerId = _perf.startTimer('ng.dirty_check', _ttl-_ttlLeft)) != false);
         digestLoop:
         do { // "traverse the scopes" loop
@@ -456,6 +461,9 @@ class Scope implements Map {
                 var value = watch.get(current);
                 var last = watch.last;
                 if (!_identical(value, last)) {
+                  if (_ttl - _ttlLeft > 2) {
+                    firedExpressions.add(watch.exp == null ? '[unknown]' : watch.exp);
+                  }
                   lastDirtyWatch = watch;
                   lastLoopLastDirtyWatch = null;
                   watch.last = value;
@@ -497,7 +505,7 @@ class Scope implements Map {
         assert(_perf.stopTimer(timerId) != false);
         if(lastDirtyWatch != null && (_ttlLeft--) == 0) {
           throw '$_ttl \$digest() iterations reached. Aborting!\n' +
-              'Watchers fired in the last 5 iterations: ${_toJson(watchLog)}';
+              'Watchers fired in the last ${_ttl - 2} iterations: ${_toJson(watchLog)}';
         }
       } while (lastDirtyWatch != null || innerAsyncQueue.length > 0);
       _perf.counters['ng.scope.watchers'] = watcherCount;

test/core/scope_spec.dart

@@ -327,6 +327,20 @@ main() {
       }));
 
 
+      it(r'should prevent infinite digest and should log firing expressions', inject((Scope $rootScope) {
+        $rootScope['a'] = 0;
+        $rootScope['b'] = 0;
+        $rootScope.$watch('a = a + 1');
+        $rootScope.$watch('b = b + 1');
+
+        expect(() {
+          $rootScope.$digest();
+        }).toThrow('Watchers fired in the last 3 iterations: ['
+            '["a = a + 1","b = b + 1"],["a = a + 1","b = b + 1"],'
+            '["a = a + 1","b = b + 1"]]');
+      }));
+
+
       it(r'should always call the watchr with newVal and oldVal equal on the first run',
           inject((Scope $rootScope) {
         var log = [];