Add gitignore for bin of plugins
Add gitignore for bin of plugins

Review URL: http://codereview.chromium.org/164258

tonyhoactive/chromedevtools,amostl/chromedevtools,amostl/chromedevtools,zhuangzhineng/chromedevtools,zhuangzhineng/chromedevtools,tonyhoactive/chromedevtools,limeditor/chromedevtools,dezelin/chromedevtools,amostl/chromedevtools,maverick1995/chromedevtools,haosu1987/chromedevtools,ParinVachhani/chromedevtools,ParinVachhani/chromedevtools,tonyhoactive/chromedevtools,limeditor/chromedevtools,maverick1995/chromedevtools,maverick1995/chromedevtools,ParinVachhani/chromedevtools,haosu1987/chromedevtools,tonyhoactive/chromedevtools,ParinVachhani/chromedevtools,zhuangzhineng/chromedevtools,maverick1995/chromedevtools,limeditor/chromedevtools,luobenyu/chromedevtools,luobenyu/chromedevtools,luobenyu/chromedevtools,amostl/chromedevtools,zhuangzhineng/chromedevtools,maverick1995/chromedevtools,ParinVachhani/chromedevtools,dezelin/chromedevtools,tonyhoactive/chromedevtools,zhuangzhineng/chromedevtools,haosu1987/chromedevtools,dezelin/chromedevtools,haosu1987/chromedevtools,limeditor/chromedevtools,dezelin/chromedevtools,luobenyu/chromedevtools,limeditor/chromedevtools,luobenyu/chromedevtools,haosu1987/chromedevtools,dezelin/chromedevtools,amostl/chromedevtools