Delete TelemetryInfo, MergedTelemetryInfo diagnostics.

docs/how-to-write-metrics.md

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      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file.
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 # How to Write Metrics
 
 Timeline-Based Measurement v2 is a system for computing metrics from traces.
 
 A TBM2 metric is a Javascript function that takes a trace Model and produces
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  * [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)
 
-### Environment Information Diagnostics
-
- * [TelemetryInfo](/tracing/tracing/value/diagnostics/telemetry_info.html):
-   This is automatically attached to every Histogram produced by telemetry.
-   Structurally, it's a class with explicit named fields.
-   Conceptually, it contains information about the origins of the trace that was
-   consumed by the metric that produced the Histogram, such as the benchmark
-   name, story name, benchmark start timestamp, etc.
-   Visually, TelemetryInfos are displayed as a table.
-
-   ![](/docs/images/how-to-write-metrics-telemetry.png)
 
 ### Other Diagnostics
 
  * [Scalar](/tracing/tracing/value/diagnostics/scalar.html):
    Metrics must not use this, since it is incapable of being merged. It is
    mentioned here for completeness. It wraps a Scalar, which is just a
    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
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  * `sum`: true
  * `min`: true
  * `max`: true
  * `nans` (number of non-numeric samples): false
  * `percentile`: []
    * Unlike the other options which are booleans, percentile is an array of
      numbers between 0 and 1. In order to upload the median, for example, a
      metric would call `histogram.customizeSummaryOptions({percentile: [0.5]})`.
 
 
-## How histogram-set-table Uses Merging and TelemetryInfo
+## How histogram-set-table Uses Merging
 
-The histogram-set-table element uses the fields of TelemetryInfo, along with the
-merging capabilities of Histograms, to allow dynamic, hierarchical
-organization of histograms:
+The histogram-set-table element uses the predefined
+[HistogramGroupings](/tracing/tracing/value/histogram_set.html), along with the
+merging capabilities of Histograms, to allow dynamic, hierarchical organization
+of histograms:
 
-* TelemetryInfo has mostly string/number (story name, story/set repeat count,
-  etc.) fields and one dict field that specifies the names of any story grouping
-  keys together with their histogram.
+* Predefined HistogramGroupings specify how to find the benchmark, story, etc.
+  that produced the Histogram.
 * After loading histograms, histogram-set-table computes categories to be
   displayed by the groupby picker at the top of the UI:
-  * Categories are fields of TelemetryInfo that have more than one value across
+  * Categories are HistogramGroupings that have more than one value across
     all histograms in the HistogramSet.
   * Instead of having one category for all story grouping keys, each grouping
     individual grouping key may be listed as a category. For example, in Page
     Cycler v2 benchmarks, the "cache_temperature" grouping key would be
     displayed as a category.
 * Choosing groups builds a hierarchy of histograms that is filled in by merging
   histograms from the bottom up. Expanding the rows of histogram-set-table, any
   leaf nodes are histograms that were loaded, and their ancestors are computed by
   merging.
-* histogram-set-table uses the "label" property of TelemetryInfo to define the
-  columns of the table.
+* histogram-set-table uses the "label" HistogramGrouping to define the columns
+  of the table.