Built-in string for vertex shaders can be empty. Nicolas handled this case in r433 but r437 overwrote it. Review URL: http://codereview.appspot.com/2233046
Built-in string for vertex shaders can be empty. Nicolas handled this case in r433 but r437 overwrote it.
Review URL: http://codereview.appspot.com/2233046

git-svn-id: a070b70d2b8c44c266a3870c0cddd9a0ee470458@439 736b8ea6-26fd-11df-bfd4-992fa37f6226

cantren/angleproject,ppy/angle,ehsan/angle,nandhanurrevanth/angle,shairai/angleproject,MSOpenTech/angle,KalebDark/angleproject,crezefire/angle,csa7mdm/angle,xin3liang/platform_external_chromium_org_third_party_angle,csa7mdm/angle,android-ia/platform_external_chromium_org_third_party_angle_dx11,ehsan/angle,themusicgod1/angleproject,ehsan/angle,ecoal95/angle,mikolalysenko/angle,android-ia/platform_external_chromium_org_third_party_angle_dx11,mybios/angle,bsergean/angle,cvsuser-chromium/chromium-third-party_angle_dx11,xin3liang/platform_external_chromium_org_third_party_angle_dx11,MIPS/external-chromium_org-third_party-angle_dx11,larsbergstrom/angle,stammen/angleproject,ghostoy/angle,android-ia/platform_external_chromium_org_third_party_angle_dx11,mybios/angle,nandhanurrevanth/angle,xin3liang/platform_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle,mlfarrell/angle,MSOpenTech/angle-win8.0,bsergean/angle,MSOpenTech/angle,KalebDark/angleproject,ghostoy/angle,KTXSoftware/angleproject,crezefire/angle,domokit/waterfall,MSOpenTech/angle-win8.0,pombreda/angleproject,mybios/angle,ppy/angle,pombreda/angleproject,xin3liang/platform_external_chromium_org_third_party_angle_dx11,android-ia/platform_external_chromium_org_third_party_angle_dx11,mrobinson/rust-angle,MIPS/external-chromium_org-third_party-angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,nandhanurrevanth/angle,cantren/angleproject,ecoal95/angle,ehsan/angle,ecoal95/angle,cvsuser-chromium/chromium-third-party_angle_dx11,vvuk/angle,xuxiandi/angleproject,xuxiandi/angleproject,jgcaaprom/android_external_chromium_org_third_party_angle,RepublicMaster/angleproject,themusicgod1/angleproject,cvsuser-chromium/chromium-third-party_angle_dx11,mikolalysenko/angle,xin3liang/platform_external_chromium_org_third_party_angle_dx11,mlfarrell/angle,vvuk/angle,RepublicMaster/angleproject,xuxiandi/angleproject,mrobinson/rust-angle,RepublicMaster/angleproject,android-ia/platform_external_chromium_org_third_party_angle,stammen/angleproject,domokit/waterfall,jgcaaprom/android_external_chromium_org_third_party_angle,vvuk/angle-old,csa7mdm/angle,KalebDark/angleproject,MIPS/external-chromium_org-third_party-angle,ecoal95/angle,KTXSoftware/angleproject,larsbergstrom/angle,KTXSoftware/angleproject,xin3liang/platform_external_chromium_org_third_party_angle,mikolalysenko/angle,ppy/angle,cantren/angleproject,jgcaaprom/android_external_chromium_org_third_party_angle,RepublicMaster/angleproject,KTXSoftware/angleproject,bsergean/angle,mrobinson/rust-angle,vvuk/angle-old,MIPS/external-chromium_org-third_party-angle,stammen/angleproject,vvuk/angle-old,ghostoy/angle,MIPS/external-chromium_org-third_party-angle_dx11,csa7mdm/angle,crezefire/angle,shairai/angleproject,mlfarrell/angle,shairai/angleproject,KTXSoftware/angleproject,mlfarrell/angle,bsergean/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,MSOpenTech/angle,xin3liang/platform_external_chromium_org_third_party_angle_dx11,xin3liang/platform_external_chromium_org_third_party_angle,larsbergstrom/angle,nandhanurrevanth/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,vvuk/angle,pombreda/angleproject,ppy/angle,shairai/angleproject,MSOpenTech/angle-win8.0,mikolalysenko/angle,MSOpenTech/angle-win8.0,crezefire/angle,jgcaaprom/android_external_chromium_org_third_party_angle,MSOpenTech/angle,themusicgod1/angleproject,cvsuser-chromium/chromium-third-party_angle_dx11,mrobinson/rust-angle,vvuk/angle-old,larsbergstrom/angle,android-ia/platform_external_chromium_org_third_party_angle,stammen/angleproject,ghostoy/angle,cantren/angleproject,pombreda/angleproject,themusicgod1/angleproject,KalebDark/angleproject,ecoal95/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle_dx11,mrobinson/rust-angle,MIPS/external-chromium_org-third_party-angle_dx11,vvuk/angle,xuxiandi/angleproject,mybios/angle