Revert of Revision Info into GenericSet

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 4fb98a5f303512a3803b17aaa7b426f2f1b4742f..d5a0e51d3187ad1f53c3f30917b9dc467862eb82 100644
--- a/docs/how-to-write-metrics.md
+++ b/docs/how-to-write-metrics.md
@@ -187,6 +187,16 @@
    Visually, TelemetryInfos are displayed as a table.
 
    ![](/docs/images/how-to-write-metrics-telemetry.png)
+
+ * [RevisionInfo](/tracing/tracing/value/diagnostics/revision_info.html):
+   This is automatically attached to every Histogram produced by telemetry.
+   Structurally, it's a class with explicit named fields. Conceptually, it
+   contains ranges of revisions of the software used to produce the trace that
+   was consumed by the metric that produced the Histogram, such as the Chromium
+   revision, v8 revision, and catapult revision. Visually, RevisionInfos are
+   displayed as a table.
+
+   ![](/docs/images/how-to-write-metrics-revision.png)
 
  * [BuildbotInfo](/tracing/tracing/value/diagnostics/buildbot_info.html):
    This is automatically attached to every Histogram produced by Chrome's