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..25d3e4ac919ff51b2751df2ae1492f5bbf8f6bad 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8608,6 +8608,20 @@ other types of suffix sets.
   <summary>The time from starting translation to the completion.</summary>
 </histogram>
 
+<histogram name="Translate.UnavailableLanguage" enum="LanguageCode">
+  <summary>
+    A language which is not available to show in the infobar in the user locale
+    but used by the translate server.

[Ilya Sherman, 2013/05/22 08:34:31]

I don't understand this description -- could you reword it?  What I'd like to
better understand is: When is this metric logged, and how should it be
interpreted?

[Takashi Toyoshima, 2013/05/23 01:26:56]

This metrics mean that Translate server returns a language code which is not
supported by l10n library in Chrome, or ICU. Basically this metrics should not
be reported. But supporting language list of Translate Server and Chrome l10n
library can be different. We should monitor it to fix broken UI potentially
caused by server side update.

[hajimehoshi, 2013/05/23 02:30:00]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Translate.UnsupportedLanguageAtInitiation" enum="LanguageCode">
+  <summary>
+    An unsupported language for the translation. This is reported when the
+    translation is going to be initialized.

[Ilya Sherman, 2013/05/22 08:34:31]

Likewise, I don't understand what the user flow is to get here.  Could you
expand or reword this comment to be a little clearer?

[Takashi Toyoshima, 2013/05/23 01:26:56]

Here, unsupported language means Google Translate doesn't support translation
for the language. This metrics is used to know which unsupported language is
important for Chrome/Google Translate.

[hajimehoshi, 2013/05/23 02:30:00]

Done.

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