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 9c66fb4af1e464fe678568f9b16229f593663b16..5aa2797accadcbac304e4099d7fd4f699d52ac0f 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -6432,6 +6432,27 @@ uploading your change for review.  These are checked by presubmit scripts.
   <int value="2" label="Has enough SCTs"/>
 </enum>
 
+<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"/>

[Benoit L, 2017/05/22 12:44:02]

This is not NoState Prefetch, right?

[mattcary, 2017/05/22 14:12:54]

I'm pretty sure it's spec prefetch (it leads to resource_prefetch_predictor).
But mostly I just wanted to count the codepath.

+  <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"/>
+  <int value="1" label="Background Tab Not Matched"/>
+  <int value="2" label="Prerender Taken"/>
+  <int value="3" label="Prerender Not Matched"/>
+</enum>
+
 <enum name="D3D11InitializeResult" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Error initializing compiler"/>