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

README

 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.
 
 The Chrome OS "metrics" package contains utilities for client-side user metric
 collection. The collected data is sent to Chrome for transport to the UMA
 server.
 
 
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 - Link the module with libmetrics (for example, by passing -lmetrics to the
   module's link command). Both libmetrics.so and libmetrics.a are built and
   installed under $SYSROOT/usr/lib/. Note that by default -lmetrics will link
   against libmetrics.so, which is preferred.
 
 - To access the metrics library API in the module, include the
   <metrics/metrics_library.h> header file. The file is installed in
   $SYSROOT/usr/include/ when the metrics library is built and installed.
 
-- The API includes two methods:
-
-  bool MetricsLibrary::SendToUMA(const std::string& name, int sample,
-                                 int min, int max, int nbuckets)
-  sends a sample for a regular (exponential) histogram.
-
-  bool MetricsLibrary::SendEnumToUMA(const std::string& name, int sample,
-                                     int max)
-  sends a sample for an enumeration (linear) histogram.
-
-  Before using these methods, a MetricsLibrary object needs to be constructed
-  and initialized through its Init method. See the complete API documentation in
-  metrics_library.h under src/platform/metrics/.
+- The API is documented in metrics_library.h under src/platform/metrics/. Before
+  using the API methods, a MetricsLibrary object needs to be constructed and
+  initialized through its Init method.
 
   For more information on the C API see c_metrics_library.h.
 
 - Samples are sent to Chrome only if the "/home/chronos/Consent To Send Stats"
   file exists (see the AreMetricsEnabled API method). Normally, this file is
   created when the user opts into metrics collection.
 
 - On the target platform, shortly after the sample is sent, it should be visible
   in Chrome through "about:histograms".
 
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 include data for older dates. If past data needs to be displayed, manual
 server-side intervention is required. In other words, one should assume that
 field data collection starts only after the histogram XML has been updated.
 
 
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 The Metrics Client: metrics_client
 ================================================================================
 
 metrics_client is a simple shell command-line utility for sending histogram
-samples. It's installed under /usr/bin on the target platform and uses
-libmetrics to send the data to Chrome. The utility is useful for generating
-metrics from shell scripts.
+samples and user actions. It's installed under /usr/bin on the target platform
+and uses libmetrics to send the data to Chrome. The utility is useful for
+generating metrics from shell scripts.
 
 For usage information and command-line options, run "metrics_client" on the
 target platform or look for "Usage:" in metrics_client.cc.
 
 
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 The Metrics Daemon: metrics_daemon
 ================================================================================
 
 metrics_daemon is a daemon that runs in the background on the target platform
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 Q. When should I use an enumeration (linear) histogram vs. a regular
    (exponential) histogram?
 
 A. Enumeration histograms should really be used only for sampling enumerated
    events and, in some cases, percentages. Normally, you should use a regular
    histogram with exponential bucket layout that provides higher resolution at
    the low end of the range and lower resolution at the high end. Regular
    histograms are generally used for collecting performance data (e.g., timing,
    memory usage, power) as well as aggregated event counts.