Handle failures allocating mapped local memory.

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 b3424e5ab89b20328db38f346211abf9e5f23639..d4914f260653b57a4ae14054be31b8c2934934bb 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -63479,6 +63479,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.LocalPersistentMemoryAllocator.Failures.Posix">
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Failures, as reported in errno, encountered while allocating local
+    persistent memory under Posix.
+  </summary>
+</histogram>
+
+<histogram name="UMA.LocalPersistentMemoryAllocator.Failures.Win">

[Alexei Svitkine (slow), 2016/09/22 16:57:13]

Please associate both of these with enums - I believe we should already have
some defined for GetLastError and errno, but you might have to look.

[bcwhite, 2016/09/22 17:25:59]

Cool.  I didn't know about those.

[Alexei Svitkine (slow), 2016/09/22 20:23:54]

Hmm, actually units="GetLastError" doesn't do anything. I checked and I guess
I'm wrong and we didn't have an enum for these.

However, I think defining it is the right thing to do. Please add it. You don't
have to fully fill it in for now, but it could be expanded over time for the
ones we see in the data on the dashboards.

For the posix errno, it seems like we do have an enum, however - OSAgnosticErrno
- so please use that. :)

Could you also switch all existing cases of units="GetLastError" and
units="errno" to these enum="" entries? Thanks!

[bcwhite, 2016/09/22 23:41:46]

It was used in a number of places, too.
Done.  I added all entries for codes 0-999.  It's easy enough to add them all
but there's at least a few thousand more defined by Microsoft.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
Done.
Done.

+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Failures, as reported by GetLastError(), encountered while allocating local
+    persistent memory under Windows.
+  </summary>
+</histogram>
+
 <histogram name="UMA.LogLoadComplete called">
   <obsolete>
     No longer tracked.