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..0d38096411b2b31ee760d39f79973aaddf5f4321
--- /dev/null
+++ b/base/files/file_tracing.cc
@@ -0,0 +1,50 @@
+// 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"
+
+namespace base {
+
+// static
+FileTracing::Provider* FileTracing::g_provider = nullptr;
+
+FileTracing::ScopedEnabler::ScopedEnabler() {
+  if (g_provider)
+    g_provider->FileTracingEnable(this);
+}
+
+FileTracing::ScopedEnabler::~ScopedEnabler() {
+  if (g_provider)
+    g_provider->FileTracingDisable(this);
+}
+
+FileTracing::ScopedTrace::ScopedTrace() : initialized_(false) {}
+
+FileTracing::ScopedTrace::~ScopedTrace() {
+  if (initialized_ && g_provider) {
+    g_provider->FileTracingEventEnd(
+        name_, &file_->trace_enabler_, file_->path_, size_);
+  }
+}
+
+bool FileTracing::ScopedTrace::ShouldInitialize() const {
+  return g_provider && g_provider->FileTracingCategoryIsEnabled();
+}
+
+void FileTracing::ScopedTrace::Initialize(
+    const char* name, File* file, int64 size) {
+  file_ = file;
+  name_ = name;
+  size_ = size;
+  initialized_ = true;
+
+  if (g_provider) {
+    g_provider->FileTracingEventBegin(
+        name_, &file_->trace_enabler_, file_->path_, size_);
+  }
+}
+
+}  // namespace base