Specify expected size when building a map.
Specify expected size when building a map.

Summary: To avoid extra resizing and allocations.

fbshipit-source-id: 069eb744a9

romanoid/buck,JoelMarcey/buck,Addepar/buck,SeleniumHQ/buck,JoelMarcey/buck,rmaz/buck,nguyentruongtho/buck,Addepar/buck,Addepar/buck,JoelMarcey/buck,nguyentruongtho/buck,romanoid/buck,romanoid/buck,shs96c/buck,rmaz/buck,brettwooldridge/buck,SeleniumHQ/buck,shs96c/buck,brettwooldridge/buck,facebook/buck,brettwooldridge/buck,facebook/buck,facebook/buck,rmaz/buck,kageiit/buck,nguyentruongtho/buck,romanoid/buck,rmaz/buck,brettwooldridge/buck,JoelMarcey/buck,brettwooldridge/buck,romanoid/buck,kageiit/buck,zpao/buck,JoelMarcey/buck,brettwooldridge/buck,romanoid/buck,SeleniumHQ/buck,kageiit/buck,JoelMarcey/buck,brettwooldridge/buck,zpao/buck,JoelMarcey/buck,SeleniumHQ/buck,kageiit/buck,SeleniumHQ/buck,rmaz/buck,brettwooldridge/buck,SeleniumHQ/buck,JoelMarcey/buck,nguyentruongtho/buck,Addepar/buck,zpao/buck,SeleniumHQ/buck,JoelMarcey/buck,romanoid/buck,shs96c/buck,shs96c/buck,romanoid/buck,rmaz/buck,SeleniumHQ/buck,Addepar/buck,SeleniumHQ/buck,JoelMarcey/buck,Addepar/buck,romanoid/buck,kageiit/buck,shs96c/buck,JoelMarcey/buck,rmaz/buck,JoelMarcey/buck,nguyentruongtho/buck,rmaz/buck,shs96c/buck,JoelMarcey/buck,shs96c/buck,kageiit/buck,nguyentruongtho/buck,nguyentruongtho/buck,rmaz/buck,shs96c/buck,SeleniumHQ/buck,facebook/buck,romanoid/buck,Addepar/buck,brettwooldridge/buck,SeleniumHQ/buck,Addepar/buck,facebook/buck,romanoid/buck,romanoid/buck,Addepar/buck,romanoid/buck,SeleniumHQ/buck,zpao/buck,shs96c/buck,shs96c/buck,rmaz/buck,Addepar/buck,SeleniumHQ/buck,brettwooldridge/buck,kageiit/buck,rmaz/buck,Addepar/buck,brettwooldridge/buck,zpao/buck,brettwooldridge/buck,rmaz/buck,Addepar/buck,Addepar/buck,brettwooldridge/buck,shs96c/buck,zpao/buck,facebook/buck,facebook/buck,shs96c/buck,rmaz/buck,shs96c/buck,zpao/buck