Add UMA reporting to CdmPromise.

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 48c4b5647bffe386679dcc80f81e46d79291c622..361ebcff27b55bc144bd57c8872976aa73eecc82 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -10343,6 +10343,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>cancelKeyRequest result using the Clear Key key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.ClearKey.createSession" enum="CdmPromiseResult">

[Ilya Sherman, 2014/08/11 21:53:48]

nit: The 'c' should probably be uppercase, to match the other histogram names. 
Ditto below.

[sandersd (OOO until July 31), 2014/08/12 16:05:51]

Done.

+  <owner>sandersd@chromium.org</owner>
+  <summary>createSession result using the Clear Key key system.</summary>

[Ilya Sherman, 2014/08/11 21:53:48]

This description is really unclear to me as someone who's not familiar with the
details of your codebase.  Is there any way that you could make it clearer,
without having to make the summary excessively verbose?

[sandersd (OOO until July 31), 2014/08/12 16:05:51]

Done.

+</histogram>
+
 <histogram name="Media.EME.ClearKey.DecryptError">
   <owner>xhwang@chromium.org</owner>
   <summary>
@@ -10389,6 +10394,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>cancelKeyRequest result using an unknown key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Unknown.createSession" enum="CdmPromiseResult">
+  <owner>sandersd@chromium.org</owner>
+  <summary>createSession result using an unknown key system.</summary>

[Ilya Sherman, 2014/08/11 21:53:48]

Ditto.

[sandersd (OOO until July 31), 2014/08/12 16:05:51]

Done.

+</histogram>
+
 <histogram name="Media.EME.Unknown.DecryptError">
   <owner>xhwang@chromium.org</owner>
   <summary>Decryption error event count using an unknown key system.</summary>
@@ -10419,6 +10429,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>cancelKeyRequest result using the Widevine key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Widevine.createSession" enum="CdmPromiseResult">
+  <owner>sandersd@chromium.org</owner>
+  <summary>createSession result using the Widevine key system.</summary>
+</histogram>
+
 <histogram name="Media.EME.Widevine.DecryptError">
   <owner>xhwang@chromium.org</owner>
   <summary>Decryption error event count using the Widevine key system.</summary>
@@ -36712,6 +36727,17 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="20" label="FutureCat (&gt;10.10), 8-bit (?)"/>
 </enum>
 
+<enum name="CdmPromiseResult" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="NotSupportedError"/>
+  <int value="2" label="InvalidStateError"/>
+  <int value="3" label="InvalidAccessError"/>
+  <int value="4" label="QuotaExceededError"/>
+  <int value="5" label="UnknownError"/>
+  <int value="6" label="ClientError"/>
+  <int value="7" label="OutputError"/>

[Ilya Sherman, 2014/08/11 21:53:48]

nit: If you prefer this formatting, that's fine; but it's also fine to include
spaces in labels -- these are intended to be human readable.

[sandersd (OOO until July 31), 2014/08/12 16:05:51]

Acknowledged.

+</enum>
+
 <enum name="CertificateChainPosition" type="int">
   <int value="0" label="Root Certificate"/>
 </enum>