Refactor Histogram relationship diagnostics.

docs/how-to-write-metrics.md

Index: docs/how-to-write-metrics.md
diff --git a/docs/how-to-write-metrics.md b/docs/how-to-write-metrics.md
index 84b6c66c3e59586d5ae66777ba2a446d8d02a702..9bab9f982ff80cb2113d63b36a63af9875555102 100644
--- a/docs/how-to-write-metrics.md
+++ b/docs/how-to-write-metrics.md
@@ -147,27 +147,12 @@ histogram.addSample(number, {name: diagnostic})
 
    ![](/docs/images/how-to-write-metrics-date-range.png)
 
-### Histogram Relationship Diagnostics
 
- * [RelatedHistogramMap](/tracing/tracing/value/diagnostics/related_histogram_map.html):
-   These are Maps from strings to references to other Histograms. Visually, they
-   are a set of HTML links where the text content of the link is the Map's
-   string key instead of the Histogram's name. One example application is when a
-   Histogram was produced not directly by a metric, but rather by merging
-   together other Histograms, then it will have a RelatedHistogramMap named
-   'mergedFrom' that refers to the Histograms that were merged by their grouping
-   key, e.g. the telemetry story name.
+### Related Histogram Name Map
 
-   ![](/docs/images/how-to-write-metrics-related-histogram-map.png)
-
- * [RelatedHistogramBreakdown](/tracing/tracing/value/diagnostics/related_histogram_breakdown.html):
-   Structurally, this is a RelatedHistogramMap, but conceptually and visually, this
-   is a Breakdown. Whereas Breakdown's stacked bar chart derives its data from
-   the numbers contained explicitly in the Breakdown, a
-   RelatedHistogramBreakdown's stacked
-   bar chart derives its data from the referenced Histograms' sums.
-
-   ![](/docs/images/how-to-write-metrics-related-histogram-breakdown.png)
+ * [RelatedNameMap](/tracing/tracing/value/diagnostics/related_name_map.html):
+   This maps from short keys to Histogram name. These are correlated with
+   Breakdowns. They are visualized as HTML links.
 
 
 ### Other Diagnostics
@@ -178,7 +163,7 @@ histogram.addSample(number, {name: diagnostic})
    unitted number. This is only to allow Histograms in other parts of the trace
    viewer to display number sample diagnostics more intelligently than
    GenericSet can. If a metric wants to display number sample diagnostics
-   intelligently, then it should use RelatedHistogramMap; if it does not want to
+   intelligently, then it should use Breakdown; if it does not want to
    monitor changes in those numbers, then the TBM2 maintainers can add a
    HistogramDiagnostic that supports merging.