add C wrapper for libmetrics

metrics_library.h

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef METRICS_LIBRARY_H_
 #define METRICS_LIBRARY_H_
 
 #include <sys/types.h>
 #include <string>
 
@@ skipping 38 matching lines @@
   // |sample| is the sample value to be recorded (1 <= |sample| < |max|).
   // |max| is the maximum value of the histogram samples.
   // 0 is the implicit underflow bucket.
   // [|max|,infinity) is the implicit overflow bucket.
   bool SendEnumToUMA(const std::string& name, int sample, int max);
 
   // Sends to Autotest and returns true on success.
   static bool SendToAutotest(const std::string& name, int value);
 
  private:
+  friend class CMetricsLibraryTest;
   friend class MetricsLibraryTest;
   FRIEND_TEST(MetricsLibraryTest, FormatChromeMessage);
   FRIEND_TEST(MetricsLibraryTest, FormatChromeMessageTooLong);
   FRIEND_TEST(MetricsLibraryTest, SendMessageToChrome);
   FRIEND_TEST(MetricsLibraryTest, SendMessageToChromeUMAEventsBadFileLocation);
 
   // Sends message of size |length| to Chrome for transport to UMA and
   // returns true on success.
   bool SendMessageToChrome(int32_t length, const char* message);
 
   // Formats a name/value message for Chrome in |buffer| and returns the
   // length of the message or a negative value on error.
   //
   // Message format is: | LENGTH(binary) | NAME | \0 | VALUE | \0 |
   //
   // The arbitrary |format| argument covers the non-LENGTH portion of the
   // message. The caller is responsible to store the \0 character
   // between NAME and VALUE (e.g. "%s%c%d", name, '\0', value).
   int32_t FormatChromeMessage(int32_t buffer_size, char* buffer,
                               const char* format, ...);
 
   const char* uma_events_file_;
 };
 
 #endif  // METRICS_LIBRARY_H_