Fix the pdfium windows slave to be an -m3 host.
Fix the pdfium windows slave to be an -m3 host.

R=friedman@chromium.org
BUG=466127

Review URL: https://codereview.chromium.org/1038493002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@294553 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build