chromium.clang: Specify OS dimensions

So that builder pools can be merged in bots.cfg

Bug: 868213
Change-Id: Iea69b964ad411c15ee5c79fb67af7dff61792449
Reviewed-on: https://chromium-review.googlesource.com/1227146Reviewed-by: Jao-ke Chin-Lee <jchinlee@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Ryan Tseng <hinoka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591482}

infra/config/global/cr-buildbucket.cfg

@@ -1481,140 +1481,174 @@ buckets {
     builders {
       name: "CFI Linux CF"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "CFI Linux ToT"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "CrWinAsan"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "CrWinAsan(dll)"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "CrWinAsanCov"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTAndroid"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTAndroid (dbg)"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTAndroid x64"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTAndroid64"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTAndroidASan"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTAndroidCFI"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinux"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinux (dbg)"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxASan"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxASanLibfuzzer"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxCoverage"
       mixins: "clang-ci"
       mixins: "clang-coverage"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxMSan"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxThinLTO"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTLinuxUBSanVptr"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "ToTMac"
       mixins: "clang-ci"
+      mixins: "mac"
     }
     builders {
       name: "ToTMac (dbg)"
       mixins: "clang-ci"
+      mixins: "mac"
     }
     builders {
       name: "ToTMacASan"
       mixins: "clang-ci"
+      mixins: "mac"
     }
     builders {
       name: "ToTMacCoverage"
       mixins: "clang-ci"
       mixins: "clang-coverage"
+      mixins: "mac"
     }
     builders {
       name: "ToTWin(dbg)"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWin(dll)"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWin64(dbg)"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWin64(dll)"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWinCFI"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWinCFI64"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTWinLibcxx64"
       mixins: "clang-ci"
+      mixins: "win"
     }
     builders {
       name: "ToTiOS"
       mixins: "clang-ci"
+      mixins: "mac"
     }
     builders {
       name: "ToTiOSDevice"
       mixins: "clang-ci"
+      mixins: "mac"
     }
     builders {
       name: "UBSanVptr Linux"
       mixins: "clang-ci"
+      mixins: "linux"
     }
     builders {
       name: "linux-win_cross-rel"
       mixins: "clang-ci"
+      mixins: "linux"
     }
 
     # chromium.gpu