Revert of Revision Info into GenericSet

docs/histogram-set-json-format.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.
 -->
 
 # HistogramSet JSON Format
 
 This document assumes familiarity with the concepts introduced in
 [how-to-write-metrics](/docs/how-to-write-metrics.md).
 
@@ skipping 115 matching lines @@
 ## Diagnostics
 
 The only field that is required for all Diagnostics, `type`, must be one of
  * `GenericSet`
  * `RelatedEventSet`
  * `Breakdown`
  * `RelatedHistogramSet`
  * `RelatedHistogramMap`
  * `RelatedHistogramBreakdown`
  * `TelemetryInfo`
+ * `RevisionInfo`
  * `BuildbotInfo`
  * `Scalar`
 
 If a Diagnostic is in the root array of the JSON, then it is shared, so it may be
 referenced by multiple Histograms. Shared Diagnostics must contain a string
 field `guid` containing a UUID.
 
 If a Diagnostic is contained in a Histogram, then it must not have a `guid`
 field.
 
 The other fields of Diagnostic dictionaries depend on `type`.
 
 ### TelemetryInfo
 
 This tracks telemetry parameters when the Histogram was produced to allow users
 to compare or merge results across similar telemetry story runs.
 
  * `benchmarkName`: string
  * `benchmarkStartMs`: number of ms since unix epoch
  * `label`: string
  * `legacyTIRLabel`: string
  * `storyDisplayName`: string
  * `storyGroupingKeys`: dictionary mapping from strings to strings
  * `storysetRepeatCounter`: number
 
+### RevisionInfo
+
+This tracks revisions of the software under test to allow users to compare or
+merge results across revisions.
+
+ * `chromiumCommitPosition`: optional integer
+ * `v8CommitPosition`: optional integer
+ * `chromium`: array of 1 or 2 strings
+ * `v8`: array of 1 or 2 strings
+ * `catapult`: array of 1 or 2 strings
+ * `angle`: array of 1 or 2 strings
+ * `skia`: array of 1 or 2 strings
+ * `webrtc`: array of 1 or 2 strings
+
 ### BuildbotInfo
 
 This tracks buildbot parameters when the Histogram was produced to allow users
 to compare or merge results across similar bots.
 
  * `displayMasterName`: string
  * `displayBotName`: string
  * `buildbotMasterName`: string
  * `buildbotName`: string
  * `buildNumber`: number
@@ skipping 50 matching lines @@
 
  * `events`: array of dictionaries containing `stableId`, `title`, `start`,
    `duration` fields of Events
 
 ### DateRange
 
 This is a Range of Dates.
 
  * `min`: Unix timestamp in ms
  * `max`: optional Unix timestamp in ms