[perfcombined2024] Disable EnableHangWatcher on Android by default.

go/perf-combined-2024-summary

Bug: 40287434
Change-Id: I3157dc730e265288f6d17f3cf742655bf709060e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6092521
Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Olivier Li <olivierli@chromium.org>
Auto-Submit: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1398810}

base/threading/hang_watcher.cc

@@ -178,11 +178,18 @@ bool ThreadTypeLoggingLevelGreaterOrEqual(HangWatcher::ThreadType thread_type,
 
 }  // namespace
 
-// Determines if the HangWatcher is activated. When false the HangWatcher
-// thread never started.
+// Enables the HangWatcher. When disabled, the HangWatcher thread should not be
+// started. Enabled by default only on platforms where the generated data is
+// used, to avoid unnecessary overhead.
 BASE_FEATURE(kEnableHangWatcher,
              "EnableHangWatcher",
-             FEATURE_ENABLED_BY_DEFAULT);
+#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC) || BUILDFLAG(IS_CHROMEOS) || \
+    BUILDFLAG(IS_LINUX)
+             FEATURE_ENABLED_BY_DEFAULT
+#else
+             FEATURE_DISABLED_BY_DEFAULT
+#endif
+);
 
 // Browser process.
 constexpr base::FeatureParam<int> kIOThreadLogLevel{

base/threading/hang_watcher_unittest.cc

@@ -9,6 +9,7 @@
 #include <optional>
 
 #include "base/barrier_closure.h"
+#include "base/feature_list.h"
 #include "base/functional/bind.h"
 #include "base/functional/callback.h"
 #include "base/functional/callback_helpers.h"
@@ -951,6 +952,9 @@ TEST_F(HangWatcherPeriodicMonitoringTest, PeriodicCallsTakePlace) {
   // invoked enough times.
   hang_watcher_.SetAfterMonitorClosureForTesting(BarrierClosure(
       kMinimumMonitorCount, base::BindLambdaForTesting([&run_loop] {
+        // This should only run if there are threads to watch.
+        EXPECT_TRUE(base::FeatureList::IsEnabled(kEnableHangWatcher));
+
         // Test condition are confirmed, stop monitoring.
         HangWatcher::StopMonitoringForTesting();
 
@@ -969,7 +973,10 @@ TEST_F(HangWatcherPeriodicMonitoringTest, PeriodicCallsTakePlace) {
   unregister_thread_closure_ =
       HangWatcher::RegisterThread(base::HangWatcher::ThreadType::kMainThread);
 
-  run_loop.Run();
+  // The "after monitor" closure only runs if there are threads to watch.
+  if (base::FeatureList::IsEnabled(kEnableHangWatcher)) {
+    run_loop.Run();
+  }
 
   // No monitored scope means no possible hangs.
   ASSERT_FALSE(hang_event_.IsSignaled());

testing/variations/fieldtrial_testing_config.json

@@ -16659,9 +16659,6 @@
                         "MojoBindingsInlineSLS",
                         "ReduceCpuUtilization2",
                         "SharedStorageAPIEnableWALForDatabase"
-                    ],
-                    "disable_features": [
-                        "EnableHangWatcher"
                     ]
                 }
             ]