New test infrastructure for producing verbose logs in failing tests.

chrome/test/base/test_log_collector_win.h

+// Copyright (c) 2012 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.
+
+// The test log collector uses Event Tracing for Windows to collect all LOG()
+// events at all levels (including all VLOG levels) from Chrome, Chrome Frame,
+// and the test executable itself for each test into a temporary log file.  At
+// the conclusion of each test, the contents of the log file are regurgitated to
+// stderr iff the test failed.  In any case, the log file is promptly deleted.
+//
+// Test executables that wish to benefit from the collector's features (to
+// produce verbose logs on test failure to aid in diagnosing flaky and/or
+// failing tests, for example) must install the collector via
+// |InstallTestLogCollector| before running tests (via RUN_ALL_TESTS(),
+// TestSuite::Run(), etc).
+
+#ifndef CHROME_TEST_BASE_TEST_LOG_COLLECTOR_WIN_H_
+#define CHROME_TEST_BASE_TEST_LOG_COLLECTOR_WIN_H_
+#pragma once
+
+namespace testing {
+class UnitTest;
+}
+
+// Installs the test log collector into |unit_test|.  The collector cannot be

[erikwright (departed), 2012/03/02 20:47:59]

I infer that testing::UnitTest does not map to a single test case as I know it?
(i.e., one instance of TEST(...) {}?).

If I'm right, can you call that out here. If I'm wrong, I really don't
understand this because I assume it is installed for the life of a test
executable.

[grt (UTC plus 2), 2012/03/02 21:22:43]

Correct.  testing::UnitTest is the process-wide singleton that owns all test
cases and all tests.  Since UnitTest is a singleton, it's actually impossible to
try to install the collector into two different unit tests, so I've removed that
bit from the comment.
See the comment at the top of the file.  Is that not sufficient?
I thought that was implied in the comment at the top; is it not clear?

[erikwright (departed), 2012/03/03 02:04:56]

The comment at the top was relatively clear. It did, after all, allow me to
infer that testing::UnitTest must represent the full test suite. I would have to
do more investigation to figure out how to get an instance of testing::UnitTest,
I suppose. I would suggest perhaps adding something along the lines of

// testing::UnitTest is the process-wide singleton that owns all test cases. It
can be retrieved via testing::UnitTest::GetInstance()

[grt (UTC plus 2), 2012/03/03 02:31:59]

I've had my head so far up Google Test's behind that I'd forgotten that I used
to not know about these details.  Thanks for the reminder.  I've added a little
more comment.

+// installed in more than one unit test, although installation in the same is
+// idempotent.
+void InstallTestLogCollector(testing::UnitTest* unit_test);
+
+#endif  // CHROME_TEST_BASE_TEST_LOG_COLLECTOR_WIN_H_