Migrate Linux CFI gl_unittests jobs to Chrome-GPU pool.

BUG=764583
TBR=dpranke@chromium.org

Change-Id: Iecad83e72eead668d7ea06f414ebed3d55c6171e
Reviewed-on: https://chromium-review.googlesource.com/664437Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501538}

testing/buildbot/chromium.fyi.json

@@ -426,7 +426,8 @@
           "dimension_sets": [
             {
               "gpu": "10de:104a",
-              "os": "Ubuntu"
+              "os": "Ubuntu",
+              "pool": "Chrome-GPU"
             }
           ]
         },
@@ -820,7 +821,8 @@
           "dimension_sets": [
             {
               "gpu": "10de:104a",
-              "os": "Ubuntu"
+              "os": "Ubuntu",
+              "pool": "Chrome-GPU"
             }
           ]
         },

testing/buildbot/chromium.memory.json

@@ -476,7 +476,8 @@
           "dimension_sets": [
             {
               "gpu": "10de:104a",
-              "os": "Ubuntu"
+              "os": "Ubuntu",
+              "pool": "Chrome-GPU"
             }
           ]
         },