implement SetWatchEvent and WaitForEvent for trace-based-tests

chrome/test/base/tracing.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_TEST_BASE_TRACING_H_
 #define CHROME_TEST_BASE_TRACING_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/time.h"
 
 namespace tracing {
 
+// Called from UI thread.
 // Begin tracing specified categories on the browser.
-// |categories| is a comma-delimited list of category wildcards.
-// A category can have an optional '-' prefix to make it an excluded category.
-// Either all categories must be included or all must be excluded.
+// |categories| is a comma-delimited list of category wildcards. A category can
+// have an optional '-' prefix to make it an excluded category. Either all
+// categories must be included or all must be excluded.
 //
 // Example: BeginTracing("test_MyTest*");
 // Example: BeginTracing("test_MyTest*,test_OtherStuff");
 // Example: BeginTracing("-excluded_category1,-excluded_category2");
 //
 // See base/debug/trace_event.h for documentation of included and excluded
 // categories.
 bool BeginTracing(const std::string& categories) WARN_UNUSED_RESULT;
 
+// Called from UI thread.
+// Specify a watch event in order to use the WaitForWatchEvent function.
+// After |num_occurrences| of the given event have been seen on a particular
+// process, WaitForWatchEvent will return.
+bool BeginTracingWithWatch(const std::string& categories,
+                           const char* category_name,

[sky, 2012/08/29 16:05:09]

Can all the args be const std::string& ? Simpler from a lifetime perspectifve.

[jbates, 2012/08/29 21:14:12]

Done.

+                           const char* event_name,
+                           int num_occurrences) WARN_UNUSED_RESULT;
+
+// Called from UI thread.
+// Wait on the event set with BeginTracingWithWatch. If non-zero, return after
+// |timeout| regardless of watch event notification. Returns true if watch event
+// occurred, false if it timed out.
+bool WaitForWatchEvent(base::TimeDelta timeout) WARN_UNUSED_RESULT;
+
+// Called from UI thread.
 // End trace and collect the trace output as a json string.
 bool EndTracing(std::string* json_trace_output) WARN_UNUSED_RESULT;
 
 }  // namespace tracing
 
 #endif  // CHROME_TEST_BASE_TRACING_H_