Added and replaced some UMAs

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 22ab0b304a14ee9ed1da3920f74429a981173668..d83f09298f2c69bbc9d5c0e1dbb7ca35c339a10d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8608,6 +8608,26 @@ other types of suffix sets.
   <summary>The time from starting translation to the completion.</summary>
 </histogram>
 
+<histogram name="Translate.UnavailableLanguage" enum="LanguageCode">
+  <summary>
+    A source language of translation which is not available from the infobar in
+    the user locale. There are two cases when this is reported. The one is when
+    the user selects auto language detection and the detected language is so
+    minor. The other is when the inforbar UI is broken and the user can choose
+    the language. The former could happen because the language set of Chrome and
+    that of translation server may differ.

[Ilya Sherman, 2013/05/23 08:30:52]

Thanks for expanding this -- much clearer now!

nit: Suggested rewording to incorporate a handful of minor edits:

"Logs the source language when a Translate infobar is shown with an unsupported
source language.  There are two cases when this can occur:  The first is when
the user selects automatic language detection and the detected language is
unsupported by the translation server because it is too minor.  The other is
when the infobar UI is broken and the user can directly choose the language. 
The former can happen because the language set of Chrome and that of the
translation server may differ."

[hajimehoshi, 2013/05/23 08:49:22]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Translate.UnsupportedLanguageAtInitiation" enum="LanguageCode">
+  <summary>
+    An unsupported language for the translation. This is reported when the
+    language detector detects the language of the webpage, but this is so minor
+    that the translation server doesn't support. We can assess how important the
+    unsupported language is for Google translate by this metrics.

[Ilya Sherman, 2013/05/23 08:30:52]

nit: Suggested rewording to incorporate a handful of minor edits:

"Logs an unsupported source language detected during initiation of the Translate
feature.  This is reported when the language detector successfully detects the
language of the webpage, but the language is not supported by the translation
server because it is too minor.  This metric allows us to assess how important
the unsupported language is for Google translate."

[hajimehoshi, 2013/05/23 08:49:22]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Translate.UserActionDuration" units="milliseconds">
   <summary>
     The time from a page content language being determined to user requesting