Add granular file tracing.

base/files/file_tracing.cc

Index: base/files/file_tracing.cc
diff --git a/base/files/file_tracing.cc b/base/files/file_tracing.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8b0767e9394ac18666e7db34eba1d2f94607210d
--- /dev/null
+++ b/base/files/file_tracing.cc
@@ -0,0 +1,43 @@
+// Copyright 2015 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 "base/files/file_tracing.h"
+
+#include "base/files/file.h"
+#include "base/files/file_path.h"
+
+namespace base {
+
+const char kFileTracingEventCategoryGroup[] = TRACE_DISABLED_BY_DEFAULT("file");
+
+ScopedFileTrace::ScopedFileTrace() : initialized_(false) {}
+
+ScopedFileTrace::~ScopedFileTrace() {
+  if (initialized_) {
+    if (size_) {
+      TRACE_EVENT_NESTABLE_ASYNC_END2(kFileTracingEventCategoryGroup, name_,
+          file_, "path", file_->unsafe_path_.AsUTF8Unsafe(), "size", size_);
+    } else {
+      TRACE_EVENT_NESTABLE_ASYNC_END1(kFileTracingEventCategoryGroup, name_,
+          file_, "path", file_->unsafe_path_.AsUTF8Unsafe());
+    }
+  }
+}
+
+void ScopedFileTrace::Initialize(const char* name, File* file, int64 size) {
+  file_ = file;
+  name_ = name;
+  size_ = size;
+  initialized_ = true;
+
+  if (size_) {
+    TRACE_EVENT_NESTABLE_ASYNC_BEGIN2(kFileTracingEventCategoryGroup, name_,
+        file_, "path", file_->unsafe_path_.AsUTF8Unsafe(), "size", size_);
+  } else {
+    TRACE_EVENT_NESTABLE_ASYNC_BEGIN1(kFileTracingEventCategoryGroup, name_,
+        file_, "path", file_->unsafe_path_.AsUTF8Unsafe());
+  }
+}
+
+}  // namespace base