Use MSVS2015 for the fyi PGO builds

scripts/slave/recipes/chromium_pgo.expected/full_chromium_fyi_Chromium_Win_PGO_Builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "taskkill"
   },
@@ skipping 90 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "buildtype=Official chrome_pgo_phase=1 component=static_library fastbuild=0 optimize=max target_arch=ia32 use_goma=0",
+      "GYP_MSVS_VERSION": "2015",
       "PATH": "[SLAVE_BUILD]\\src\\out\\Release;%(PATH)s"
     },
     "name": "gclient Runhooks: Instrumentation phase."
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys\nfrom common import chromium_utils\n\nchromium_utils.RemoveFilesWildcards(sys.argv[1], root=sys.argv[2])\n",
       "*.pg[cd]",
@@ skipping 369 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
-      "GYP_DEFINES": "buildtype=Official chrome_pgo_phase=2 component=static_library fastbuild=0 optimize=max target_arch=ia32 use_goma=0"
+      "GYP_DEFINES": "buildtype=Official chrome_pgo_phase=2 component=static_library fastbuild=0 optimize=max target_arch=ia32 use_goma=0",
+      "GYP_MSVS_VERSION": "2015"
     },
     "name": "gclient Runhooks: Optimization phase."
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[pgo]\\resources\\increase_pgomgr_stack_size.py",
       "[DEPOT_TOOLS]\\win_toolchain\\vs2013_files\\VC\\bin\\amd64_x86"
     ],
@@ skipping 34 matching lines @@
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "package build"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]