fix(ChangeDetection): chain expressions evaluate to the last expression (codegen)

fixes angular#4782
Closes angular#5892

Author: vicb

modules/angular2/src/core/change_detection/codegen_logic_util.ts

@@ -103,7 +103,7 @@ export class CodegenLogicUtil {
         break;
 
       case RecordType.Chain:
-        rhs = 'null';
+        rhs = `${getLocalName(protoRec.args[protoRec.args.length - 1])}`;
         break;
 
       default:

modules/angular2/test/core/change_detection/change_detector_config.ts

@@ -438,6 +438,7 @@ var _availableEventDefinitions = [
   '(event)="a[0]=\$event"',
   // '(event)="\$event=1"',
   '(event)="a=a+1; a=a+1;"',
+  '(event)="true; false"',
   '(event)="false"',
   '(event)="true"',
   '(event)="true ? a = a + 1 : a = a + 1"',

modules/angular2/test/core/change_detection/change_detector_spec.ts

@@ -1358,6 +1358,10 @@ export function main() {
           val = _createChangeDetector('(event)="true"', d, null);
           res = val.changeDetector.handleEvent("event", 0, event);
           expect(res).toBe(true);
+
+          val = _createChangeDetector('(event)="true; false"', d, null);
+          res = val.changeDetector.handleEvent("event", 0, event);
+          expect(res).toBe(false);
         });
 
         it('should support short-circuiting', () => {