Add support for user actions to the metrics library and the metrics clients.

c_metrics_library.cc

Index: c_metrics_library.cc
diff --git a/c_metrics_library.cc b/c_metrics_library.cc
index e97f9ac264059040213a319c8005da45842ea1b8..3450918c4757ec9e48a10128142af5da9e4355ae 100644
--- a/c_metrics_library.cc
+++ b/c_metrics_library.cc
@@ -43,6 +43,14 @@ extern "C" int CMetricsLibrarySendEnumToUMA(CMetricsLibrary handle,
   return lib->SendEnumToUMA(std::string(name), sample, max);
 }
 
+extern "C" int CMetricsLibrarySendUserActionToUMA(CMetricsLibrary handle,
+                                                  const char* action) {
+  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);
+  if (lib == NULL)
+    return 0;
+  return lib->SendUserActionToUMA(std::string(action));
+}
+
 extern "C" int CMetricsLibraryAreMetricsEnabled(CMetricsLibrary handle) {
   MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);
   if (lib == NULL)