Remove clock resolution page load histograms.

These were temporary metrics intended to understand whether high/low
resolution clocks adversely impact page load metrics. After collecting a few
months of data it was determined that clock resolution doesn't adversely
impact our metrics, and it that these histograms were no longer needed.

BUG=394757

Review-Url: https://codereview.chromium.org/2155143003
Cr-Commit-Position: refs/heads/master@{#406143}

chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc

@@ -198,11 +198,6 @@ const char kHistogramLoadTypeParseStartForwardBack[] =
 const char kHistogramLoadTypeParseStartNewNavigation[] =
     "PageLoad.ParseTiming.NavigationToParseStart.LoadType.NewNavigation";
 
-const char kHistogramFirstContentfulPaintHigh[] =
-    "PageLoad.Timing2.NavigationToFirstContentfulPaint.HighResolutionClock";
-const char kHistogramFirstContentfulPaintLow[] =
-    "PageLoad.Timing2.NavigationToFirstContentfulPaint.LowResolutionClock";
-
 const char kHistogramFirstBackground[] =
     "PageLoad.Timing2.NavigationToFirstBackground";
 const char kHistogramFirstForeground[] =
@@ -582,15 +577,6 @@ void CorePageLoadMetricsObserver::RecordTimingHistograms(
             timing.first_contentful_paint, info)) {
       PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaint,
                           timing.first_contentful_paint.value());
-      // Bucket these histograms into high/low resolution clock systems. This
-      // might point us to directions that will de-noise some UMA.
-      if (base::TimeTicks::IsHighResolution()) {
-        PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaintHigh,
-                            timing.first_contentful_paint.value());
-      } else {
-        PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaintLow,
-                            timing.first_contentful_paint.value());
-      }
       PAGE_LOAD_HISTOGRAM(
           internal::kHistogramParseStartToFirstContentfulPaint,
           timing.first_contentful_paint.value() - timing.parse_start.value());

tools/metrics/histograms/histograms.xml

@@ -95081,6 +95081,12 @@ To add a new entry, add it with any value and run test to compute valid value.
 </histogram_suffixes>
 
 <histogram_suffixes name="ClockResolution" separator=".">
+  <obsolete>
+    These were temporary metrics intended to understand whether high/low
+    resolution clocks adversely impact page load metrics. After collecting a few
+    months of data it was determined that clock resolution doesn't adversely
+    impact our metrics, and that these histograms were no longer needed.
+  </obsolete>
   <suffix name="HighResolutionClock"
       label="base::TimeTicks::IsHighResolution() is true for this measurement"/>
   <suffix name="LowResolutionClock"