Wire up OOM exception to the sad tab page.

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 ca096ba7e740a748cd70b7e244e51facbb1ee469..308374118af4cdf4ad0e663b398940a8e14ff007 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -59176,6 +59176,29 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Tabs.SadTab.OomCreated">

[Alexei Svitkine (slow), 2016/07/25 20:39:00]

Add units="sad tabs" here and below. (Or something similar).

[Will Harris, 2016/07/25 20:47:53]

Done. Used "tabs" as that's used elsewhere.

+  <owner>wfh@chromium.org</owner>
+  <summary>
+    Cumulative number of times a tab crashed with &quot;Aw, Snap!&quot;,
+    recorded once per tab oom event.  For example, a user who ran out of memory
+    in 3 tabs will record a count in the 1 bin, 2 bin, and 3 bin.  Thus each bin
+    N is the number of sessions where users experienced N or more oom events.
+    The user may not have actually seen the sad tab page, as it might have been
+    an inactive tab. Compare to Tabs.SadTab.OomDisplayed.
+  </summary>
+</histogram>
+
+<histogram name="Tabs.SadTab.OomDisplayed">
+  <owner>wfh@chromium.org</owner>
+  <summary>
+    Cumulative number of times a tab ran out of memory with &quot;Aw,
+    Snap!&quot; and the user saw the page, recorded once per tab oom event.  For
+    example, a user who ran out of memory in 3 tabs will record a count in the 1
+    bin, 2 bin, and 3 bin.  Thus each bin N is the number of sessions where
+    users experienced N or more oom events.  Compare to Tabs.SadTab.OomCreated.
+  </summary>
+</histogram>
+
 <histogram name="Tabs.SadTab.ReloadCount">
   <owner>jamescook@chromium.org</owner>
   <summary>