Add histograms for temperatures and thermal states.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index f879a89c876967194b6b5b4b2422d07978306e67..dedcf310c5365d9f8e34595b0c5e2a6b482f5a2f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -24621,6 +24621,86 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Temperature reading at sensor 9 (PECI) taken every 30s.</summary>
 </histogram>
 
+<histogram name="Platform.Thermal.Temperature.Cpu.0" units="Celsius">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    Temperature reading at sensor 0 of the CPU collected every few seconds (may
+    vary between devices).
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Temperature.Wifi0" units="Celsius">

[Ilya Sherman, 2015/01/22 02:53:47]

nit: You use ".0" for CPU readings, but just "0" for Wifi.  I suggest keeping
those consistent.

[mka, 2015/01/23 19:03:32]

In the case of the Wifi interface the 0 is the index of the interface, for the
CPU it's the sensor number. Said that, for now a single sensor is used and I
can't predict if that will ever change. Putting the index is an attempt of being
prepared for more than one sensor. I'm not sure this is actually the right thing
to do or if we should rather have a temperature Cpu and adapt the histograms
when necessary, possibly deprecating the one without indexes.

+  <owner>mka@chromium.org</owner>
+  <summary>
+    Temperature reading at wireless interface 0 collected every few seconds (may
+    vary between devices).
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Temperature.Wifi1" units="Celsius">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    Temperature reading at wireless interface 1 collected every few seconds (may
+    vary between devices).
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Temperature.Wifi2" units="Celsius">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    Temperature reading at wireless interface 2 collected every few seconds (may

[Ilya Sherman, 2015/01/22 02:53:47]

What defines wireless interface "1" vs. "2", etc.?  It might be clearer to use
more semantically contentful names.

[mka, 2015/01/23 19:03:32]

It's the interface number/name assigned by the OS. In our team we discussed more
semantic schemes but didn't encounter a consistent and future proof one. Also
for the engineers who will most often look at these histograms the
hardware/system related names are probably more meaningful.

+    vary between devices).
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Zone.Cpu.States" units="Thermal state">

[Ilya Sherman, 2015/01/22 02:53:47]

Would it make sense for the state to be an enum?  You could use a sparse
histogram and hash a string, for example, if you wanted to be able to assign
flexible labels to the enum.

[mka, 2015/01/23 19:03:32]

I considered initially to use labels like "warm", "hot", "critically hot", ...
but discarded the idea because the number of states would be limited by the
number of reasonable classifications of the thermal states in English language.

+  <owner>mka@chromium.org</owner>
+  <summary>
+    State of the thermal zone of the CPU collected every second. State depends
+    on device, higher state corresponds to a higher temperature.
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Zone.Wifi0.States" units="Thermal state">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    State of the thermal zone of wireless interface 0 collected every second.
+    State depends on device, higher state corresponds to a higher temperature.
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Zone.Wifi1.States" units="Thermal state">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    State of the thermal zone of wireless interface 1 collected every second.
+    State depends on device, higher state corresponds to a higher temperature.
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Platform.Thermal.Zone.Wifi2.States" units="Thermal state">
+  <owner>mka@chromium.org</owner>
+  <summary>
+    State of the thermal zone of wireless interface 2 collected every second.
+    State depends on device, higher state corresponds to a higher temperature.
+
+    This metric is specific to ChromeOS.
+  </summary>
+</histogram>
+
 <histogram name="Platform.TPM.DictionaryAttackCounter">
   <owner>dkrahn@chromium.org</owner>
   <summary>