PRESUBMIT: Ignore external_bin/.
PRESUBMIT: Ignore external_bin/.

This is created for the external gsutil since r293320, and was creating
needless churn in presubmit tests when it is present.

R=pgervais@chromium.org,hinoka@google.com
BUG=434422

Review URL: https://codereview.chromium.org/831913003

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@293574 0039d316-1c4b-4281-b951-d872f2087c98

liaorubei/depot_tools,G-P-S/depot_tools,duanwujie/depot_tools,aleonliao/depot_tools,withtone/depot_tools,G-P-S/depot_tools,eatbyte/depot_tools,xuyuhan/depot_tools,withtone/depot_tools,azunite/chrome_build,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,CoherentLabs/depot_tools,aleonliao/depot_tools,withtone/depot_tools,mlufei/depot_tools,duanwujie/depot_tools,G-P-S/depot_tools,ajohnson23/depot_tools,xuyuhan/depot_tools,ajohnson23/depot_tools,duongbaoduy/gtools,disigma/depot_tools,azureplus/chromium_depot_tools,npe9/depot_tools,kaiix/depot_tools,fanjunwei/depot_tools,sarvex/depot-tools,disigma/depot_tools,chinmaygarde/depot_tools,fracting/depot_tools,disigma/depot_tools,hsharsha/depot_tools,fracting/depot_tools,gcodetogit/depot_tools,npe9/depot_tools,eatbyte/depot_tools,Midrya/chromium,SuYiling/chrome_depot_tools,liaorubei/depot_tools,xuyuhan/depot_tools,eatbyte/depot_tools,fanjunwei/depot_tools,airtimemedia/depot_tools,azunite/chrome_build,chinmaygarde/depot_tools,sarvex/depot-tools,gcodetogit/depot_tools,hsharsha/depot_tools,primiano/depot_tools,duongbaoduy/gtools,mlufei/depot_tools,duongbaoduy/gtools,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,airtimemedia/depot_tools,primiano/depot_tools,liaorubei/depot_tools,sarvex/depot-tools,airtimemedia/depot_tools,hsharsha/depot_tools,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,npe9/depot_tools,airtimemedia/depot_tools,azunite/chrome_build,CoherentLabs/depot_tools,azureplus/chromium_depot_tools,eatbyte/depot_tools,fanjunwei/depot_tools,xuyuhan/depot_tools,primiano/depot_tools,fracting/depot_tools,fanjunwei/depot_tools,sarvex/depot-tools,chinmaygarde/depot_tools,Midrya/chromium,liaorubei/depot_tools,SuYiling/chrome_depot_tools,ajohnson23/depot_tools,azureplus/chromium_depot_tools,npe9/depot_tools,mlufei/depot_tools,aleonliao/depot_tools,G-P-S/depot_tools,SuYiling/chrome_depot_tools,kaiix/depot_tools,kaiix/depot_tools,gcodetogit/depot_tools,duanwujie/depot_tools,Midrya/chromium