[gn] Add trace entries for loading and blocking on imports

tools/gn/trace.h

 // Copyright (c) 2013 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 TOOLS_GN_TRACE_H_
 #define TOOLS_GN_TRACE_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 
 class Label;
 
 namespace base {
 class CommandLine;
 class FilePath;
 }
 
 class TraceItem {
  public:
   enum Type {
     TRACE_SETUP,
     TRACE_FILE_LOAD,
     TRACE_FILE_PARSE,
     TRACE_FILE_EXECUTE,
     TRACE_FILE_WRITE,
+    TRACE_IMPORT_LOAD,
+    TRACE_IMPORT_BLOCK,
     TRACE_SCRIPT_EXECUTE,
     TRACE_DEFINE_TARGET,
     TRACE_ON_RESOLVED,
-    TRACE_CHECK_HEADER,  // One file.
+    TRACE_CHECK_HEADER,   // One file.
     TRACE_CHECK_HEADERS,  // All files.
   };
 
   TraceItem(Type type,
             const std::string& name,
             base::PlatformThreadId thread_id);
   ~TraceItem();
 
   Type type() const { return type_; }
   const std::string& name() const { return name_; }
@@ skipping 38 matching lines @@
   void Done();
 
  private:
   TraceItem* item_;
   bool done_;
 };
 
 // Call to turn tracing on. It's off by default.
 void EnableTracing();
 
+// Returns whether tracing is enabled.
+bool TracingEnabled();
+
 // Adds a trace event to the log. Takes ownership of the pointer.
 void AddTrace(TraceItem* item);
 
 // Returns a summary of the current traces, or the empty string if tracing is
 // not enabled.
 std::string SummarizeTraces();
 
 // Saves the current traces to the given filename in JSON format.
 void SaveTraces(const base::FilePath& file_name);
 
 #endif  // TOOLS_GN_TRACE_H_