Add a use counter and histogram to FileReaderSync.

third_party/WebKit/Source/core/fileapi/FileReaderSync.cpp

 /*
  * Copyright (C) 2010 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 #include "core/fileapi/FileReaderSync.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "core/dom/DOMArrayBuffer.h"
 #include "core/fileapi/Blob.h"
 #include "core/fileapi/FileError.h"
 #include "core/fileapi/FileReaderLoader.h"
+#include "platform/Histogram.h"
 
 namespace blink {
 
-FileReaderSync::FileReaderSync() {}
+namespace {
+// These values are written to logs.  New enum values can be added, but existing
+// enums must never be renumbered or deleted and reused.
+enum class WorkerType {
+  DEDICATED_WORKER = 0,
+  SHARED_WORKER = 1,
+  SERVICE_WORKER = 2,
+  OTHER = 3,

[Mark P, 2017/02/10 22:56:42]

OTHER sounds like a miscellaneous bucket.  If so, please put that first.  See
(recently-added) last paragraph in this section:
https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/metrics/histo...

[Marijn Kruisselbrink, 2017/02/10 23:17:28]

Good point, done.

+  MAX
+};
+}  // namespace
+
+FileReaderSync::FileReaderSync(ExecutionContext* context) {
+  WorkerType type = WorkerType::OTHER;
+  if (context->isDedicatedWorkerGlobalScope())
+    type = WorkerType::DEDICATED_WORKER;
+  else if (context->isSharedWorkerGlobalScope())
+    type = WorkerType::SHARED_WORKER;
+  else if (context->isServiceWorkerGlobalScope())
+    type = WorkerType::SERVICE_WORKER;
+  DEFINE_THREAD_SAFE_STATIC_LOCAL(
+      EnumerationHistogram, workerTypeHistogram,
+      new EnumerationHistogram("FileReaderSync.WorkerType",
+                               static_cast<int>(WorkerType::MAX)));
+  workerTypeHistogram.count(static_cast<int>(type));
+}
 
 DOMArrayBuffer* FileReaderSync::readAsArrayBuffer(
     ScriptState* scriptState,
     Blob* blob,
     ExceptionState& exceptionState) {
   ASSERT(blob);
 
   std::unique_ptr<FileReaderLoader> loader =
       FileReaderLoader::create(FileReaderLoader::ReadAsArrayBuffer, nullptr);
   startLoading(scriptState->getExecutionContext(), *loader, *blob,
@@ skipping 44 matching lines @@
 void FileReaderSync::startLoading(ExecutionContext* executionContext,
                                   FileReaderLoader& loader,
                                   const Blob& blob,
                                   ExceptionState& exceptionState) {
   loader.start(executionContext, blob.blobDataHandle());
   if (loader.errorCode())
     FileError::throwDOMException(exceptionState, loader.errorCode());
 }
 
 }  // namespace blink