Added arm test spec.

Will be used by chromium_trybot_arm recipe.

R=mseaborn@chromium.org, phajdan.jr@chromium.org
BUG=359338

Review URL: https://codereview.chromium.org/246623009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269655 0039d316-1c4b-4281-b951-d872f2087c98

testing/buildbot/chromium_arm.json

+[
+  {
+    "description": ["These tests will be run on an ARM device, which is fairly",
+                    "slow, that's why we run a much smaller set of tests.",
+                    "We run NaCl tests specifically because NaCl contains",
+                    "a lot of architecture-specific code"],
+    "test": "browser_tests",
+    "args": "--gtest-filter='*NaCl*'"
+  }
+]