Report LatencyInfo through trace buffer

ui/events/latency_info.h

Index: ui/events/latency_info.h
diff --git a/ui/events/latency_info.h b/ui/events/latency_info.h
index 8bf56100dfd84324c1dc9b40923244ba580f2400..9547ad1af26685042bfc7dd9afc08e64d42081ea 100644
--- a/ui/events/latency_info.h
+++ b/ui/events/latency_info.h
@@ -9,11 +9,31 @@
 #include <utility>
 
 #include "base/basictypes.h"
+#include "base/debug/trace_event.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/events_export.h"
 
 namespace ui {
 
+// This class is for converting latency info to trace buffer friendly format.
+class LatencyInfoTracedValue : public base::debug::ConvertableToTraceFormat {

[nduca, 2013/10/01 21:43:44]

i think you can put this implementation in the cc file since its not visible
elsewhere

[Yufeng Shen (Slow to review), 2013/10/04 00:29:51]

Done.

+ public:
+  static scoped_ptr<ConvertableToTraceFormat> FromValue(
+      base::Value* value);
+
+  virtual ~LatencyInfoTracedValue();
+
+  virtual void AppendAsTraceFormat(std::string* out) const OVERRIDE;
+
+ private:
+  explicit LatencyInfoTracedValue(base::Value* value);
+
+  scoped_ptr<base::Value> value_;
+
+  DISALLOW_COPY_AND_ASSIGN(LatencyInfoTracedValue);
+};
+
 enum LatencyComponentType {
   // Timestamp when the input event is sent from RenderWidgetHost to renderer.
   INPUT_EVENT_LATENCY_RWH_COMPONENT,

[nduca, 2013/10/01 21:43:44]

lets prefix this with a name to indicate that it begins the flow

[Yufeng Shen (Slow to review), 2013/10/04 00:29:51]

Done.

@@ -30,9 +50,14 @@ enum LatencyComponentType {
   INPUT_EVENT_LATENCY_ORIGINAL_COMPONENT,
   // Timestamp when the UI event is created.
   INPUT_EVENT_LATENCY_UI_COMPONENT,
-  // Timestamp when the event is acked from renderer. This is currently set
-  // only for touch events.
-  INPUT_EVENT_LATENCY_ACKED_COMPONENT
+  // Timestamp when the mouse event is acked from renderer.
+  INPUT_EVENT_LATENCY_ACKED_MOUSE_COMPONENT,

[nduca, 2013/10/01 21:43:44]

lets try calling these FINISH_ or TERMINAL ... latency_finished_at_blahblah for
example 

[Rick Byers, 2013/10/03 13:12:41]

Is the idea that these will always be terminal?  Won't even the common case of
touch scrolling have a ACKED_TOUCH, ACKED_GESTURE AND a FRAME_SWAP?  

[Yufeng Shen (Slow to review), 2013/10/04 00:29:51]

Done.

[Yufeng Shen (Slow to review), 2013/10/04 00:29:51]

As offline talk, we will only allow one terminal component.
so for a touch event. See the comments in the new patch.

+  // Timestamp when the touch event is acked from renderer.
+  INPUT_EVENT_LATENCY_ACKED_TOUCH_COMPONENT,
+  // Timestamp when the gesture event is acked from renderer.
+  INPUT_EVENT_LATENCY_ACKED_GESTURE_COMPONENT,
+  // Timestamp when the frame is swapped.
+  INPUT_EVENT_LATENCY_FRAME_SWAP_COMPONENT,
 };
 
 struct EVENTS_EXPORT LatencyInfo {
@@ -56,6 +81,13 @@ struct EVENTS_EXPORT LatencyInfo {
 
   ~LatencyInfo();
 
+  // When the LatencyInfo is considered to have finished its lifetime, call
+  // this function. |terminal_component| is added to indicate when & why
+  // this function is called. And then the whole latency info is reported
+  // to system (i.e. dumped to trace buffer).
+  void Report(LatencyComponentType terminal_component);
+  scoped_ptr<base::debug::ConvertableToTraceFormat> AsTraceableData() const;

[jdduke (slow), 2013/10/01 23:45:31]

AsTraceableData() appears to be used only be Report().  Could you make make it a
static/scoped method inside latency_info.cc?  Or make it private? You could then
have it take the "terminal" latency component as an argument, which in turn
would allow you to make Report(...) const, perhaps something like

AsTraceableData(const LatencyInfo& latency, LatencyComponentType
terminal_component);

[Yufeng Shen (Slow to review), 2013/10/04 00:29:51]

moved into cc file as a global function. 

+
   // Merges the contents of another LatencyInfo into this one.
   void MergeWith(const LatencyInfo& other);
 
@@ -86,9 +118,6 @@ struct EVENTS_EXPORT LatencyInfo {
   void Clear();
 
   LatencyMap latency_components;
-
-  // This represents the final time that a frame is displayed it.
-  base::TimeTicks swap_timestamp;
 };
 
 }  // namespace ui