Custom Tabs: add speculation status histograms.

tools/metrics/histograms/enums.xml

Index: tools/metrics/histograms/enums.xml
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index 94c4b4888b53967aa52466e11271813b592908b2..23b6e2d53d6a26f85d179719f28247a68ac9e843 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -6454,6 +6454,26 @@ uploading your change for review.  These are checked by presubmit scripts.
   <int value="7" label="10.0"/>
   <int value="8" label="10.1"/>
   <int value="9" label="11.0"/>
+
+<enum name="CustomTabsSpeculationStatusOnStart" type="int">
+  <int value="0"
+      label="Speculation allowed. If started, the kind will also be recorded"/>
+  <int value="1" label="Prefetch kind of speculation started"/>
+  <int value="2" label="Prerender kind of speculation started"/>
+  <int value="3" label="Background Tab kind of speculation started"/>
+  <int value="4" label="Prerender speculation allowed, but not started"/>
+  <int value="5" label="Aborted: Device class"/>
+  <int value="6" label="Aborted: Block 3rd party cookies"/>
+  <int value="7" label="Aborted: Network prediction disabled"/>
+  <int value="8" label="Aborted: Data reduction enabled"/>
+  <int value="9" label="Aborted: Network metered"/>
+</enum>
+
+<enum name="CustomTabsSpeculationStatusOnSwap" type="int">
+  <int value="0" label="Background Tab Taken"/>

[Mark P, 2017/05/30 22:09:53]

Taken == swapped-in?

[mattcary, 2017/05/31 08:15:40]

Done.

+  <int value="1" label="Background Tab Not Matched"/>

[Mark P, 2017/05/30 22:09:53]

"not matched" == ?
no longer needed?

[mattcary, 2017/05/31 08:15:40]

Currently a background tab that's not matched is discarded, but that might not
be true in the future. I think the current wording is more accurate and
future-proof.

[Mark P, 2017/06/01 05:19:35]

I find the meaning of "not matched" unintuitive.  What wrong with "not swapped
in"?

[mattcary, 2017/06/06 14:39:23]

There may in the future be multiple reasons for a speculation to not be swapped
in; currently not matching is the only reason but in the future there may be
more. With the current wording we would not have to change the enum label if
more failure-to-swap reasons are added. Let me know if it would be preferable to
do it that way.

[Mark P, 2017/06/06 18:25:50]

Okay.

[mattcary, 2017/06/07 11:55:47]

Acknowledged.

+  <int value="2" label="Prerender Taken"/>
+  <int value="3" label="Prerender Not Matched"/>
 </enum>
 
 <enum name="D3D11InitializeResult" type="int">