base: Reenable CpuAffinityTest on non-Nexus5 bots

The test is flaky on Nexus 5 because it seems that something else in the
system affects the affinity of our process, but seems to pass on other
devices.

Cq-Include-Trybots: luci.chromium.try:android-lollipop-arm-rel
Bug: 1113964
Change-Id: Iae40d8513c177cae1929a425a32899ca4f28419c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2467900Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816713}

base/cpu_affinity_posix_unittest.cc

@@ -75,8 +75,7 @@ class TestThread : public PlatformThread::Delegate {
 }  // namespace
 
 #if defined(OS_ANDROID)
-// Flaky on Android. crbug.com/1113964
-#define MAYBE_SetThreadCpuAffinityMode DISABLED_SetThreadCpuAffinityMode
+#define MAYBE_SetThreadCpuAffinityMode SetThreadCpuAffinityMode
 #else
 // The test only considers Android device hardware models at the moment. Some
 // CrOS devices on the waterfall have asymmetric CPUs that aren't covered. The
@@ -102,6 +101,10 @@ TEST(CpuAffinityTest, MAYBE_SetThreadCpuAffinityMode) {
   } else if (device_model == "Pixel 3a" || device_model == "Pixel 3a XL") {
     expected_little_cores = 6;
     EXPECT_LT(expected_little_cores, expected_total_cores);
+  } else if (device_model == "Nexus 5") {
+    // On our Nexus 5 bots, something else in the system seems to set affinity
+    // for the test process, making these tests flaky (crbug.com/1113964).
+    return;
   }
 
   TestThread thread;