Add OS to SkiaCT dimensions.

This will make it much easier to experiment with upgrading the OS to
Debian-9.1 without causing failures on master.

No-Try: true
Change-Id: Id43b055841ec3ceb42133c9dd7b630f12d1b45c6
Reviewed-on: https://skia-review.googlesource.com/31001
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
diff --git a/infra/bots/gen_tasks.go b/infra/bots/gen_tasks.go
index f775ef6..d72f803 100644
--- a/infra/bots/gen_tasks.go
+++ b/infra/bots/gen_tasks.go
@@ -568,8 +568,11 @@
 // generated chain of tasks, which the Job should add as a dependency.
 func ctSKPs(b *specs.TasksCfgBuilder, name string) string {
 	b.MustAddTask(name, &specs.TaskSpec{
-		CipdPackages:     []*specs.CipdPackage{},
-		Dimensions:       []string{"pool:SkiaCT"},
+		CipdPackages: []*specs.CipdPackage{},
+		Dimensions: []string{
+			"pool:SkiaCT",
+			"os:Ubuntu-14.04",
+		},
 		ExecutionTimeout: 24 * time.Hour,
 		ExtraArgs: []string{
 			"--workdir", "../../..", "ct_skps",
diff --git a/infra/bots/tasks.json b/infra/bots/tasks.json
index 02a4e19..4cb3d62 100644
--- a/infra/bots/tasks.json
+++ b/infra/bots/tasks.json
@@ -7699,7 +7699,8 @@
     },
     "Perf-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-CT_BENCH_1k_SKPs": {
       "dimensions": [
-        "pool:SkiaCT"
+        "pool:SkiaCT",
+        "os:Ubuntu-14.04"
       ],
       "execution_timeout_ns": 86400000000000,
       "extra_args": [
@@ -7721,7 +7722,8 @@
     },
     "Perf-Ubuntu-GCC-Golo-GPU-GT610-x86_64-Release-CT_BENCH_1k_SKPs": {
       "dimensions": [
-        "pool:SkiaCT"
+        "pool:SkiaCT",
+        "os:Ubuntu-14.04"
       ],
       "execution_timeout_ns": 86400000000000,
       "extra_args": [
@@ -14511,7 +14513,8 @@
     },
     "Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-CT_DM_100k_SKPs": {
       "dimensions": [
-        "pool:SkiaCT"
+        "pool:SkiaCT",
+        "os:Ubuntu-14.04"
       ],
       "execution_timeout_ns": 86400000000000,
       "extra_args": [
@@ -14533,7 +14536,8 @@
     },
     "Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-CT_DM_1m_SKPs": {
       "dimensions": [
-        "pool:SkiaCT"
+        "pool:SkiaCT",
+        "os:Ubuntu-14.04"
       ],
       "execution_timeout_ns": 86400000000000,
       "extra_args": [
@@ -14555,7 +14559,8 @@
     },
     "Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-CT_IMG_DECODE_100k_SKPs": {
       "dimensions": [
-        "pool:SkiaCT"
+        "pool:SkiaCT",
+        "os:Ubuntu-14.04"
       ],
       "execution_timeout_ns": 86400000000000,
       "extra_args": [