net/http: stop timeout timer if user cancels a request
net/http: stop timeout timer if user cancels a request

Change-Id: I84faeae69f294b9a70e545faac6a070feba67770
Reviewed-on: https://go-review.googlesource.com/28074
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

linux-on-ibm-z/go,CAFxX/go,golang/go,suncycheng/go,linux-on-ibm-z/go,nawawi/go,codestation/go,ImJasonH/go,polyverse-security/go,suncycheng/go,polyverse-security/go,CAFxX/go,polyverse-security/go,Cofyc/go,derekmarcotte/go,josharian/go,goodlang/good,CAFxX/go,cloudflare/go,linux-on-ibm-z/go,momchil-velikov/go,akutz/go,polyverse-security/go,christopher-henderson/Go,Cofyc/go,josharian/go,nawawi/go,akutz/go,josharian/go,Cofyc/go,linux-on-ibm-z/go,goodlang/good,derekmarcotte/go,akutz/go,Cofyc/go,cloudflare/go,momchil-velikov/go,linux-on-ibm-z/go,goodlang/good,codestation/go,vsekhar/elastic-go,nawawi/go,nawawi/go,akutz/go,CAFxX/go,goodlang/good,derekmarcotte/go,josharian/go,akutz/go,goodlang/good,momchil-velikov/go,golang/go,nawawi/go,Cofyc/go,goodlang/good,derekmarcotte/go,vsekhar/elastic-go,ImJasonH/go,derekmarcotte/go,nawawi/go,golang/go,goodlang/good,derekmarcotte/go,golang/go,vsekhar/elastic-go,momchil-velikov/go,derekmarcotte/go,vsekhar/elastic-go,linux-on-ibm-z/go,akutz/go,CAFxX/go,suncycheng/go,cloudflare/go,codestation/go,cloudflare/go,momchil-velikov/go,suncycheng/go,polyverse-security/go,codestation/go,linux-on-ibm-z/go,linux-on-ibm-z/go,suncycheng/go,codestation/go,cloudflare/go,vsekhar/elastic-go,suncycheng/go,akutz/go,ImJasonH/go,codestation/go,nawawi/go,josharian/go,ImJasonH/go,cloudflare/go,josharian/go,ImJasonH/go,momchil-velikov/go,polyverse-security/go,vsekhar/elastic-go,ImJasonH/go,ImJasonH/go,codestation/go,CAFxX/go,vsekhar/elastic-go,Cofyc/go,cloudflare/go,polyverse-security/go,golang/go,golang/go,Cofyc/go,josharian/go,golang/go,nawawi/go,josharian/go,vsekhar/elastic-go,CAFxX/go,golang/go,momchil-velikov/go,CAFxX/go,akutz/go,momchil-velikov/go,ImJasonH/go,Cofyc/go,derekmarcotte/go,suncycheng/go,codestation/go,suncycheng/go,cloudflare/go,goodlang/good,polyverse-security/go