Remove suffixes OnBattery, NotOnBattery from FCP

This change removes histogram suffixes
PageLoad.PaintTiming.NavigationToFirstContentfulPaint.OnBattery and
PageLoad.PaintTiming.NavigationToFirstContentfulPaint.NotOnBattery,
which allowed the filtering of FirstContentfulPaint measurements by
whether the system was on battery or wall power during page load.

This was used to filter FirstContentfulPaint regressions for
battery-specific Finch experiment SlowDCTimerInterruptsWin, which is
now on Stable. Because the experiment is finished and I'm not aware
of any other users, this histogram can be removed.

Change-Id: I78a6a2026596cb9aaa0783129ee3f4d8034fc039
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468337Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Jesse McKenna <jessemckenna@google.com>
Cr-Commit-Position: refs/heads/master@{#817559}

components/page_load_metrics/browser/observers/core/uma_page_load_metrics_observer.cc

@@ -11,7 +11,6 @@
 
 #include "base/feature_list.h"
 #include "base/metrics/histogram_macros.h"
-#include "base/power_monitor/power_monitor.h"
 #include "components/page_load_metrics/browser/observers/core/largest_contentful_paint_handler.h"
 #include "components/page_load_metrics/browser/page_load_metrics_util.h"
 #include "content/public/common/process_type.h"
@@ -187,11 +186,6 @@ const char kHistogramParseBlockedOnScriptExecutionDocumentWrite[] =
 const char kHistogramFirstContentfulPaintNoStore[] =
     "PageLoad.PaintTiming.NavigationToFirstContentfulPaint.NoStore";
 
-const char kHistogramFirstContentfulPaintOnBattery[] =
-    "PageLoad.PaintTiming.NavigationToFirstContentfulPaint.OnBattery";
-const char kHistogramFirstContentfulPaintNotOnBattery[] =
-    "PageLoad.PaintTiming.NavigationToFirstContentfulPaint.NotOnBattery";
-
 const char kHistogramFirstContentfulPaintHiddenWhileFlushing[] =
     "PageLoad.PaintTiming.NavigationToFirstContentfulPaint.HiddenWhileFlushing";
 
@@ -522,14 +516,6 @@ void UmaPageLoadMetricsObserver::OnFirstContentfulPaintInPage(
                           timing.paint_timing->first_contentful_paint.value());
     }
 
-    if (base::PowerMonitor::IsOnBatteryPower()) {
-      PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaintOnBattery,
-                          timing.paint_timing->first_contentful_paint.value());
-    } else {
-      PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaintNotOnBattery,
-                          timing.paint_timing->first_contentful_paint.value());
-    }
-
     // TODO(bmcquade): consider adding a histogram that uses
     // UserInputInfo.user_input_event.
     if (GetDelegate().GetUserInitiatedInfo().browser_initiated ||

components/page_load_metrics/browser/observers/core/uma_page_load_metrics_observer_unittest.cc

@@ -43,14 +43,6 @@ class UmaPageLoadMetricsObserverTest
   void SetUp() override {
     page_load_metrics::PageLoadMetricsObserverContentTestHarness::SetUp();
     page_load_metrics::LargestContentfulPaintHandler::SetTestMode(true);
-
-    base::PowerMonitor::Initialize(
-        std::make_unique<base::PowerMonitorTestSource>());
-  }
-
-  void TearDown() override {
-    base::PowerMonitor::ShutdownForTesting();
-    page_load_metrics::PageLoadMetricsObserverContentTestHarness::TearDown();
   }
 
   void OnCpuTimingUpdate(RenderFrameHost* render_frame_host,

tools/metrics/histograms/histograms_xml/histogram_suffixes_list.xml

@@ -7902,6 +7902,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram_suffixes>
 
 <histogram_suffixes name="IsOnBattery" separator=".">
+  <obsolete>
+    Removed 2020-10.
+  </obsolete>
   <suffix name="NotOnBattery" label="System is on external power."/>
   <suffix name="OnBattery" label="System is on battery power."/>
   <affected-histogram