Update the libmetrics API to match the new Chrome interface.

src/platform/metrics/metrics_library.h

Index: src/platform/metrics/metrics_library.h
diff --git a/src/platform/metrics/metrics_library.h b/src/platform/metrics/metrics_library.h
index ebc972cae4b897f193d80ee4e0b9897f887c7727..5977e724cf1871573e62cb2181204c07c4b2a836 100644
--- a/src/platform/metrics/metrics_library.h
+++ b/src/platform/metrics/metrics_library.h
@@ -16,13 +16,25 @@
 
 // TODO(sosa@chromium.org): Add testing for send methods
 
-// Library used to send metrics both Autotest and Chrome
+// Library used to send metrics both Autotest and Chrome.
 class MetricsLibrary {
  public:
-  // Sends histogram data to Chrome and returns true on success.
-  static bool SendToChrome(std::string name, int value);
+  // Sends histogram data to Chrome for transport to UMA and returns
+  // true on success. This method results in the equivalent of an
+  // asynchronous non-blocking RPC to UMA_HISTOGRAM_CUSTOM_COUNTS
+  // inside Chrome (see base/histogram.h).
+  //
+  // |sample| is the sample value to be recorded (|min| <= |sample| < |max|).
+  // |min| is the minimum value of the histogram samples (|min| > 0).
+  // |max| is the maximum value of the histogram samples.
+  // |nbuckets| is the number of histogram buckets.
+  // [0,min) is the implicit underflow bucket.
+  // [|max|,infinity) is the implicit overflow bucket.
+  static bool SendToChrome(const std::string& name, int sample,
+                           int min, int max, int nbuckets);
+
   // Sends to Autotest and returns true on success.
-  static bool SendToAutotest(std::string name, int value);
+  static bool SendToAutotest(const std::string& name, int value);
 };
 
 #endif /* METRICS_LIBRARY_H_ */