Add various trace events for tracing startup

@abarth

sky/engine/core/script/dart_controller.cc

@@ -88,6 +88,8 @@ void DartController::DidLoadMainLibrary(String name) {
 }
 
 void DartController::DidLoadSnapshot() {
+  TRACE_EVENT0("flutter", "DartController::DidLoadSnapshot");
+
   DCHECK(Dart_CurrentIsolate() == nullptr);
   snapshot_loader_ = nullptr;
 

sky/engine/core/script/dart_init.cc

@@ -281,6 +281,7 @@ bool IsRunningPrecompiledCode() {
 #endif  // DART_ALLOW_DYNAMIC_RESOLUTION
 
 void InitDartVM() {
+  TRACE_EVENT0("flutter", "InitDartVM");
   dart::bin::BootstrapDartIo();
 
   bool enable_checked_mode = RuntimeEnabledFeatures::dartCheckedModeEnabled();

sky/engine/web/Sky.cpp

@@ -46,6 +46,7 @@
 #include "sky/engine/wtf/text/AtomicString.h"
 #include "sky/engine/wtf/text/TextEncoding.h"
 #include "sky/engine/wtf/WTF.h"
+#include "base/trace_event/trace_event.h"
 
 namespace blink {
 
@@ -115,6 +116,8 @@ static void cryptographicallyRandomValues(unsigned char* buffer, size_t length)
 
 void initialize(Platform* platform)
 {
+    TRACE_EVENT0("flutter", "blink::initialize");
+
     ASSERT(!s_webKitInitialized);
     s_webKitInitialized = true;
 

sky/shell/platform/android/org/domokit/sky/shell/SkyActivity.java

@@ -12,6 +12,7 @@ import android.view.View;
 import android.view.WindowManager;
 
 import org.chromium.base.PathUtils;
+import org.chromium.base.TraceEvent;
 import org.chromium.mojom.sky.EventType;
 import org.chromium.mojom.sky.InputEvent;
 
@@ -113,6 +114,8 @@ public class SkyActivity extends Activity {
       * Override this function to customize startup behavior.
       */
     protected void onSkyReady() {
+        TraceEvent.instant("SkyActivity.onSkyReady");
+
         if (loadIntent(getIntent())) {
             return;
         }

sky/shell/ui/engine.cc

@@ -170,6 +170,8 @@ void Engine::RunFromLibrary(const std::string& name) {
 void Engine::RunFromSnapshotStream(
     const std::string& name,
     mojo::ScopedDataPipeConsumerHandle snapshot) {
+  TRACE_EVENT0("flutter", "Engine::RunFromSnapshotStream");
+
   sky_view_ = blink::SkyView::Create(this);
   sky_view_->CreateView(blink::WebString::fromUTF8(name));
   sky_view_->RunFromSnapshot(blink::WebString::fromUTF8(name), snapshot.Pass());
@@ -201,6 +203,8 @@ void Engine::RunFromFile(const mojo::String& main,
 }
 
 void Engine::RunFromBundle(const mojo::String& path) {
+  TRACE_EVENT0("flutter", "Engine::RunFromBundle");
+
   AssetUnpackerJob* unpacker = new AssetUnpackerJob(
       mojo::GetProxy(&root_bundle_), base::WorkerPool::GetTaskRunner(true));
   std::string path_str = path;