Implement about:tracing UI for the sampling profiler (Chromium part)

components/tracing/child_trace_message_filter.cc

Index: components/tracing/child_trace_message_filter.cc
diff --git a/components/tracing/child_trace_message_filter.cc b/components/tracing/child_trace_message_filter.cc
index 154903a15d0725d6c72aa594165076d4cb5bea72..b875c05416a395581ae0d587efcc503c2c965803 100644
--- a/components/tracing/child_trace_message_filter.cc
+++ b/components/tracing/child_trace_message_filter.cc
@@ -34,6 +34,12 @@ bool ChildTraceMessageFilter::OnMessageReceived(const IPC::Message& message) {
   IPC_BEGIN_MESSAGE_MAP(ChildTraceMessageFilter, message)
     IPC_MESSAGE_HANDLER(TracingMsg_BeginTracing, OnBeginTracing)
     IPC_MESSAGE_HANDLER(TracingMsg_EndTracing, OnEndTracing)
+    IPC_MESSAGE_HANDLER(TracingMsg_BeginContinuousSamplingTracing,
+                        OnBeginContinuousSamplingTracing)
+    IPC_MESSAGE_HANDLER(TracingMsg_EndContinuousSamplingTracing,
+                        OnEndContinuousSamplingTracing)
+    IPC_MESSAGE_HANDLER(TracingMsg_ShowContinuousSamplingTracing,
+                        OnShowContinuousSamplingTracing)
     IPC_MESSAGE_HANDLER(TracingMsg_GetTraceBufferPercentFull,
                         OnGetTraceBufferPercentFull)
     IPC_MESSAGE_HANDLER(TracingMsg_SetWatchEvent, OnSetWatchEvent)
@@ -77,6 +83,29 @@ void ChildTraceMessageFilter::OnEndTracing() {
   channel_->Send(new TracingHostMsg_EndTracingAck(category_groups));
 }
 
+void ChildTraceMessageFilter::OnBeginContinuousSamplingTracing(
+    base::TimeTicks browser_time) {
+  TraceLog::GetInstance()->SetContinuousSamplingEnabled();
+}
+
+void ChildTraceMessageFilter::OnEndContinuousSamplingTracing() {
+  TraceLog::GetInstance()->SetContinuousSamplingDisabled();
+}
+
+void ChildTraceMessageFilter::OnShowContinuousSamplingTracing() {
+  // Flush will generate one or more callbacks to
+  // OnContinuousSamplingTraceDataCollected. It's important that the last
+  // OnContinuousSamplingTraceDataCollected gets called before
+  // ShowContinuousSamplingTracingAck below. We are already on the IO thread,
+  // so the OnContinuousSamplingTraceDataCollected calls will not be deferred.
+  TraceLog::GetInstance()->FlushContinuousSamplingTracing(
+      base::Bind(&ChildTraceMessageFilter::
+                 OnContinuousSamplingTraceDataCollected,
+                 this));
+
+  channel_->Send(new TracingHostMsg_ShowContinuousSamplingTracingAck());
+}
+
 void ChildTraceMessageFilter::OnGetTraceBufferPercentFull() {
   float bpf = TraceLog::GetInstance()->GetBufferPercentFull();
 
@@ -105,6 +134,20 @@ void ChildTraceMessageFilter::OnTraceDataCollected(
       events_str_ptr->data()));
 }
 
+void ChildTraceMessageFilter::OnContinuousSamplingTraceDataCollected(
+    const scoped_refptr<base::RefCountedString>& events_str_ptr) {
+  if (!ipc_message_loop_->BelongsToCurrentThread()) {
+    ipc_message_loop_->PostTask(FROM_HERE,
+        base::Bind(&ChildTraceMessageFilter::
+                   OnContinuousSamplingTraceDataCollected,
+                   this,
+                   events_str_ptr));
+    return;
+  }
+  channel_->Send(new TracingHostMsg_ContinuousSamplingTraceDataCollected(
+      events_str_ptr->data()));
+}
+
 void ChildTraceMessageFilter::OnTraceNotification(int notification) {
   if (!ipc_message_loop_->BelongsToCurrentThread()) {
     ipc_message_loop_->PostTask(FROM_HERE,