Introduce OutputFormatter interface and wire it through PageTestResults.

tools/telemetry/telemetry/results/output_formatter.py

Index: tools/telemetry/telemetry/results/output_formatter.py
diff --git a/tools/telemetry/telemetry/results/output_formatter.py b/tools/telemetry/telemetry/results/output_formatter.py
new file mode 100644
index 0000000000000000000000000000000000000000..cd6e330b84aacde40d475a9d9e254a9d7f8c79bc
--- /dev/null
+++ b/tools/telemetry/telemetry/results/output_formatter.py
@@ -0,0 +1,33 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+class OutputFormatter(object):
+  """A formatter for PageTestResults.
+
+  An OutputFormatter takes PageTestResults, formats the results
+  (telemetry.value.Value instances), and output the formatted results
+  in the given output stream.
+
+  Examples of output formatter: CsvOutputFormatter produces results in
+  CSV format."""
+
+  def __init__(self, output_stream):
+    """Constructs a new formatter that writes to the output_stream.
+
+    Args:
+      output_stream: The stream to write the formatted output to.
+    """
+    self.output_stream = output_stream
+
+  def Format(self, page_test_results):
+    """Formats the given PageTestResults into the output stream.
+
+    This will be called once at the end of a benchmark.
+
+    Args:
+      page_test_results: A PageTestResults object containing all results
+         from the current benchmark run.
+    """
+    raise NotImplementedError()