Revert "[TaskScheduler] Temporarily disable heartbeat latency metrics on...

Revert "[TaskScheduler] Temporarily disable heartbeat latency metrics on Android to bisect power regression"

This reverts commit 548db201.

Reason for revert: regression had recovered on its own and this CL doesn't seem to help further : https://chromeperf.appspot.com/group_report?sid=3b04a394179538536eb72ebc4c7a33913ff5dcc85145d95666f5aea61823d770

Original change's description:
> [TaskScheduler] Temporarily disable heartbeat latency metrics on Android to bisect power regression
> 
> R=​fdoray@chromium.org
> 
> Bug: 848255
> Change-Id: Ic47d338fb15e0bf3579ecd9d1acca67099c6d570
> Reviewed-on: https://chromium-review.googlesource.com/1137849
> Reviewed-by: Robert Liao <robliao@chromium.org>
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#576158}

TBR=gab@chromium.org,robliao@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 848255
Change-Id: Ie402a1ec2381f296863522bcf9ba7c387648df6d
Reviewed-on: https://chromium-review.googlesource.com/1148481Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577581}

base/task_scheduler/service_thread.cc

@@ -13,7 +13,6 @@
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/task_scheduler/task_tracker.h"
 #include "base/task_scheduler/task_traits.h"
-#include "build/build_config.h"
 
 namespace base {
 namespace internal {
@@ -37,9 +36,6 @@ void ServiceThread::Init() {
   // environment, do not perform the heartbeat report in that case since it
   // relies on such an environment.
   if (task_tracker_ && TaskScheduler::GetInstance()) {
-// Seemingly causing power regression on Android, disable to see if truly at
-// fault : https://crbug.com/848255
-#if !defined(OS_ANDROID)
     // Compute the histogram every hour (with a slight offset to drift if that
     // hour tick happens to line up with specific events). Once per hour per
     // user was deemed sufficient to gather a reliable metric.
@@ -51,7 +47,6 @@ void ServiceThread::Init() {
                                           : g_heartbeat_for_testing,
         BindRepeating(&ServiceThread::PerformHeartbeatLatencyReport,
                       Unretained(this)));
-#endif
   }
 }
 

base/task_scheduler/service_thread_unittest.cc

@@ -52,18 +52,10 @@ TEST(TaskSchedulerServiceThreadTest, MAYBE_StackHasIdentifyingFrame) {
   service_thread.FlushForTesting();
 }
 
-#if defined(OS_ANDROID)
-// The heartbeat latency report has been temporarily disabled on Android per
-// https://crbug.com/848255.
-#define MAYBE_HeartbeatLatencyReport DISABLED_HeartbeatLatencyReport
-#else
-#define MAYBE_HeartbeatLatencyReport HeartbeatLatencyReport
-#endif
-
 // Integration test verifying that a service thread running in a fully
 // integrated TaskScheduler environment results in reporting
 // HeartbeatLatencyMicroseconds metrics.
-TEST(TaskSchedulerServiceThreadIntegrationTest, MAYBE_HeartbeatLatencyReport) {
+TEST(TaskSchedulerServiceThreadIntegrationTest, HeartbeatLatencyReport) {
   ServiceThread::SetHeartbeatIntervalForTesting(TimeDelta::FromMilliseconds(1));
 
   TaskScheduler::SetInstance(