Refactor Histogram relationship diagnostics.

docs/metrics-results-ui.md

 <!-- Copyright 2016 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file.
 -->
 
 # Metrics Results UI
 
 This document assumes familiarity with the concepts introduced in
 [how-to-write-metrics](/docs/how-to-write-metrics.md).
 
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 diagnostics for the selected Histogram bins.
 
 ![Show full Histogram data for a cell.
 ](/docs/images/metrics-results-ui-show-histogram.png)
 
 Sample diagnostics may include Breakdown diagnostics, which indicate relative
 sizes of component metrics for the selected samples.
 
 ![Breakdowns](/docs/images/how-to-write-metrics-breakdown.png)
 
-Other Histogram diagnostics may include RelatedHistogramBreakdown diagnostics,
-which indicate relative sizes of component metrics over all samples.
-
-![RelatedHistogramBreakdowns](/docs/images/how-to-write-metrics-related-histogram-breakdown.png)
-
 For more about summation metrics, see [Diagnostic
 Metrics](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/speed/diagnostic_metrics.md#Summation-Diagnostics).
 
 ## The Groupby-picker
 
 The `groupby-picker` sits just above the table and allows you to control how
 Histograms are grouped into the Grouping Tree.
 
 Grouping keys include
  * Histogram name
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 ### The Show All Checkbox
 
 By default, this checkbox is unchecked so that the table only displays
 Histograms that are source nodes in the metric graphical model.
 Check this checkbox in order to show all Histograms, including those that are
 not source nodes in the metric graphical model.
 
 ![Show All Histograms checkbox.
 ](/docs/images/metrics-results-ui-show-all.png)