Add UMA stat to track usage of Chrome for Linux accross different window managers

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 32499f100af6094c24c9572bf9348c0e9067dd43..db67616054a0e397d38fc272a92e15e6191f35f2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9344,6 +9344,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>The version of glibc used. (Linux only)</summary>
 </histogram>
 
+<histogram name="Linux.WindowManager" enum="LinuxWindowManagerName">
+  <owner>pkotwicz@chromium.org</owner>
+  <summary>The window manager used. (Linux only)</summary>

[Ilya Sherman, 2014/06/11 20:07:55]

Please document when this metric is recorded.

+</histogram>
+
 <histogram name="LocalDiscovery.ClientRestartAttempts">
   <owner>noamsml@chromium.org</owner>
   <owner>vitalybuka@chromium.org</owner>
@@ -38598,6 +38603,21 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="10" label="2.19"/>
 </enum>
 
+<enum name="LinuxWindowManagerName" type="int">
+  <int value="0" label="Other"/>
+  <int value="1" label="Blackbox"/>
+  <int value="2" label="Chrome OS"/>
+  <int value="3" label="Compiz"/>
+  <int value="4" label="Enlightment"/>
+  <int value="5" label="IceWM"/>
+  <int value="6" label="KWin"/>
+  <int value="7" label="Metacity"/>
+  <int value="8" label="Muffin"/>
+  <int value="9" label="Mutter"/>
+  <int value="10" label="Openbox"/>
+  <int value="11" label="Xfwm4"/>
+</enum>
+
 <enum name="LoadType" type="int">
   <int value="0" label="UNDEFINED_LOAD">Not yet initialized</int>
   <int value="1" label="RELOAD">User pressed reload</int>