问题：
E:\PDFium>git clone https://pdfium.googlesource.com/pdfium
Cloning into 'pdfium'...
fatal: unable to access 'https://pdfium.googlesource.com/pdfium/': Failed connect to pdfium.googlesource.com:443; No error
解决：
git config --global http.proxy http://proxy.com:1234
git config --global https.proxy http://proxy.com:1234
git config --global http.sslverify false
转自：http://ricksu.blog.163.com/blog/static/18906433820125294929508/
参考：http://infong.net/config-proxy-for-git/
我使用本机上的小软件翻墙，所以设置为
E:\PDFium>git config --global http.proxy http://127.0.0.1:8580
E:\PDFium>git config --global https.proxy https://127.0.0.1:8580
E:\PDFium>git config --global http.SSLVERIFY false
