Re-land first pass BackgroundTracingManager.

content/public/browser/background_tracing_reactive_config.h

Index: content/public/browser/background_tracing_reactive_config.h
diff --git a/content/public/browser/background_tracing_reactive_config.h b/content/public/browser/background_tracing_reactive_config.h
new file mode 100644
index 0000000000000000000000000000000000000000..12f45524470c063f73302ac375c1c09985cb8482
--- /dev/null
+++ b/content/public/browser/background_tracing_reactive_config.h
@@ -0,0 +1,37 @@
+// Copyright 2015 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 CONTENT_PUBLIC_BROWSER_BACKGROUND_REACTIVE_TRACING_CONFIG_H_
+#define CONTENT_PUBLIC_BROWSER_BACKGROUND_REACTIVE_TRACING_CONFIG_H_
+
+#include "content/public/browser/background_tracing_config.h"
+
+namespace content {
+
+// BackgroundTracingReactiveConfig holds trigger rules for use during
+// reactive tracing. Tracing will be not be enabled immediately, rather
+// the BackgroundTracingManager will wait for a trigger to occur, and
+// enable tracing at that point. Tracing will be finalized later, either
+// after some time has elapsed or the trigger occurs again.
+struct CONTENT_EXPORT BackgroundTracingReactiveConfig
+    : public BackgroundTracingConfig {
+ public:
+  BackgroundTracingReactiveConfig();
+
+  enum RuleType { TRACE_ON_TRIGGER_UNTIL_10S_OR_NEXT_TRIGGER_OR_FULL };

[no sievers, 2015/05/14 21:25:17]

nit: so this is TRACE_ON_MANUAL_TRIGGER_...?

[shatch, 2015/05/15 21:00:51]

Done.

+  struct TracingRule {
+    RuleType type;
+    std::string trigger_name;
+    CategoryPreset category_preset;

[no sievers, 2015/05/14 21:25:17]

Aha, that's interesting that you allow multiple categories in this mode.
Why not in the other mode then?

[shatch, 2015/05/15 21:00:51]

This mode (reactive) doesn't start tracing until an event triggers it, so you
can wait and then get the categories for that event.

The other mode has tracing enabled already, which means you had to set the
categories ahead of time.

+  };
+
+  std::vector<TracingRule> configs;
+
+ protected:
+  ~BackgroundTracingReactiveConfig() override;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_BACKGROUND_REACTIVE_TRACING_CONFIG_H_