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

tools/gn/trace.cc

 // 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.
 
 #include "tools/gn/trace.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <map>
@@ skipping 152 matching lines @@
       AddTrace(item_);
     }
   }
 }
 
 void EnableTracing() {
   if (!trace_log)
     trace_log = new TraceLog;
 }
 
+bool TracingEnabled() {
+  return !!trace_log;
+}
+
 void AddTrace(TraceItem* item) {
   trace_log->Add(item);
 }
 
 std::string SummarizeTraces() {
   if (!trace_log)
     return std::string();
 
   std::vector<TraceItem*> events = trace_log->events();
 
@@ skipping 13 matching lines @@
         break;
       case TraceItem::TRACE_SCRIPT_EXECUTE:
         script_execs.push_back(event);
         break;
       case TraceItem::TRACE_CHECK_HEADERS:
         check_headers.push_back(event);
         break;
       case TraceItem::TRACE_CHECK_HEADER:
         headers_checked++;
         break;
+      case TraceItem::TRACE_IMPORT_LOAD:
+      case TraceItem::TRACE_IMPORT_BLOCK:
       case TraceItem::TRACE_SETUP:
       case TraceItem::TRACE_FILE_LOAD:
       case TraceItem::TRACE_FILE_WRITE:
       case TraceItem::TRACE_DEFINE_TARGET:
       case TraceItem::TRACE_ON_RESOLVED:
         break;  // Ignore these for the summary.
     }
   }
 
   std::ostringstream out;
@@ skipping 58 matching lines @@
         break;
       case TraceItem::TRACE_FILE_PARSE:
         out << "\"parse\"";
         break;
       case TraceItem::TRACE_FILE_EXECUTE:
         out << "\"file_exec\"";
         break;
       case TraceItem::TRACE_FILE_WRITE:
         out << "\"file_write\"";
         break;
+      case TraceItem::TRACE_IMPORT_LOAD:
+        out << "\"import_load\"";
+        break;
+      case TraceItem::TRACE_IMPORT_BLOCK:
+        out << "\"import_block\"";
+        break;
       case TraceItem::TRACE_SCRIPT_EXECUTE:
         out << "\"script_exec\"";
         break;
       case TraceItem::TRACE_DEFINE_TARGET:
         out << "\"define\"";
         break;
       case TraceItem::TRACE_ON_RESOLVED:
         out << "\"onresolved\"";
         break;
       case TraceItem::TRACE_CHECK_HEADER:
@@ skipping 25 matching lines @@
     }
     out << "}";
   }
 
   out << "]}";
 
   std::string out_str = out.str();
   base::WriteFile(file_name, out_str.data(),
                        static_cast<int>(out_str.size()));
 }