Perfetto: Start tracing as soon as the Consumer endpoint is created

Previously this was done in the OnConnect() callback, but it turns
out this is called via PostTask() so if tracing gets disabled immediately
after it's enabled, the disable call can come in between and causes
test failures due to the StopAndFlush callback never happening.

Bug: 873073,872631
Change-Id: I343060c5e4b9d66575e6b8fe71a28cc9b706a429
Reviewed-on: https://chromium-review.googlesource.com/1171658Reviewed-by: Siddhartha S <ssid@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582758}

content/browser/tracing/tracing_controller_browsertest.cc

@@ -487,9 +487,7 @@ IN_PROC_BROWSER_TEST_F(TracingControllerTest,
 }
 
 // TODO(crbug.com/871770): Disabled for failing on ASAN.
-// TODO(crbug.com/872631): Disabled on Android as flaky.
-// TODO(crbug.com/873073): Disabled on Linux as flaky.
-#if defined(ADDRESS_SANITIZER) || defined(OS_ANDROID) || defined(OS_LINUX)
+#if defined(ADDRESS_SANITIZER)
 #define MAYBE_EnableAndStopTracingWithEmptyFile \
   DISABLED_EnableAndStopTracingWithEmptyFile
 #else
@@ -517,9 +515,7 @@ IN_PROC_BROWSER_TEST_F(TracingControllerTest,
 }
 
 // TODO(crbug.com/871770): Disabled for failing on ASAN.
-// TODO(crbug.com/872631): Disabled on Android as flaky.
-// TODO(crbug.com/873073): Disabled on Linux as flaky.
-#if defined(ADDRESS_SANITIZER) || defined(OS_ANDROID) || defined(OS_LINUX)
+#if defined(ADDRESS_SANITIZER)
 #define MAYBE_DoubleStopTracing DISABLED_DoubleStopTracing
 #else
 #define MAYBE_DoubleStopTracing DoubleStopTracing

services/tracing/perfetto/json_trace_exporter.cc

@@ -184,11 +184,7 @@ JSONTraceExporter::JSONTraceExporter(const std::string& config,
                                      perfetto::TracingService* service)
     : config_(config), metadata_(std::make_unique<base::DictionaryValue>()) {
   consumer_endpoint_ = service->ConnectConsumer(this);
-}
-
-JSONTraceExporter::~JSONTraceExporter() = default;
 
-void JSONTraceExporter::OnConnect() {
   // Start tracing.
   perfetto::TraceConfig trace_config;
   trace_config.add_buffers()->set_size_kb(4096 * 100);
@@ -207,6 +203,10 @@ void JSONTraceExporter::OnConnect() {
   consumer_endpoint_->EnableTracing(trace_config);
 }
 
+JSONTraceExporter::~JSONTraceExporter() = default;
+
+void JSONTraceExporter::OnConnect() {}
+
 void JSONTraceExporter::OnDisconnect() {}
 
 void JSONTraceExporter::OnTracingDisabled() {