Add histogram to track number of .nexe launches, normalized against opening new tabs.
BUG=914 (http://code.google.com/p/nativeclient/issues/detail?id=914)
TEST=none
  Relied on trybots and manually checking "about:histograms"

Review URL: http://codereview.chromium.org/4065005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64261 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/base.gypi b/base/base.gypi
index 4b15ec5..248a21ea 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -148,6 +148,8 @@
           'message_pump_win.h',
           'metrics/histogram.cc',
           'metrics/histogram.h',
+          'metrics/nacl_histogram.cc',
+          'metrics/nacl_histogram.h',		  
           'metrics/stats_counters.cc',
           'metrics/stats_counters.h',
           'metrics/stats_table.cc',