Fixing pixel2 device_os dimension

NOTRY=true
TBR=ashleymarie@chromium.org

Bug: 817872
Change-Id: Ib6b85a069c46e0e1a1f2c03a08dbea95d2ed1d41
Reviewed-on: https://chromium-review.googlesource.com/1044294Reviewed-by: Emily Hanley <eyaich@chromium.org>
Commit-Queue: Emily Hanley <eyaich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556053}

testing/buildbot/chromium.perf.fyi.json

@@ -720,7 +720,7 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
-              "device_is": "O",
+              "device_os": "O",
               "device_type": "walleye",
               "os": "Android",
               "pool": "chrome.test.perf-fyi"
@@ -768,7 +768,7 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
-              "device_is": "O",
+              "device_os": "O",
               "device_type": "walleye",
               "os": "Android",
               "pool": "chrome.test.perf-webview-fyi"

tools/perf/core/perf_data_generator.py

@@ -1037,7 +1037,7 @@ NEW_PERF_RECIPE_FYI_TESTERS = {
         'pool': 'chrome.test.perf-webview-fyi',
         'os': 'Android',
         'device_type': 'walleye',
-        'device_is': 'O'
+        'device_os': 'O'
       },
       'device_ids': [
       ],
@@ -1054,7 +1054,7 @@ NEW_PERF_RECIPE_FYI_TESTERS = {
         'pool': 'chrome.test.perf-fyi',
         'os': 'Android',
         'device_type': 'walleye',
-        'device_is': 'O'
+        'device_os': 'O'
       },
       'device_ids': [
       ],