Update tracing framework to optionally use a ringbuffer.

base/debug/trace_event_unittest.cc

Index: base/debug/trace_event_unittest.cc
diff --git a/base/debug/trace_event_unittest.cc b/base/debug/trace_event_unittest.cc
index 0e3be874009bace9bd7a44009c5da2463415eaf4..5fb90407c65df90867fbeff5b563616b47be1a03 100644
--- a/base/debug/trace_event_unittest.cc
+++ b/base/debug/trace_event_unittest.cc
@@ -1531,6 +1531,8 @@ TEST_F(TraceEventTestFixture, TraceOptionsParsing) {
 
   EXPECT_EQ(TraceLog::RECORD_UNTIL_FULL,
             TraceLog::TraceOptionsFromString("record-until-full"));
+  EXPECT_EQ(TraceLog::RECORD_CONTINUOUSLY,
+            TraceLog::TraceOptionsFromString("record-continuously"));
 }
 
 TEST_F(TraceEventTestFixture, TraceSampling) {
@@ -1606,5 +1608,7 @@ TEST_F(TraceEventCallbackTest, TraceEventCallback) {
   EXPECT_EQ("event2", collected_events_[1]);
 }
 
+// TODO(dsinclair): Continuous Tracing unit test.
+
 }  // namespace debug
 }  // namespace base