Enable building pdf_use_skia in the standalone build.

skia/ext/google_logging.cc

+// Copyright (c) 2012 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.
+
+// This file provides integration with Google-style "base/logging.h" assertions
+// for Skia SkASSERT. If you don't want this, you can link with another file
+// that provides integration with the logging of your choice.
+
+#include <stdio.h>
+
+#include "third_party/skia/include/core/SkTypes.h"
+
+void SkDebugf_FileLine(const char* file,
+                       int line,
+                       bool fatal,
+                       const char* format,
+                       ...) {
+  va_list ap;
+  va_start(ap, format);
+
+  fprintf(stderr, "%s:%d ", file, line);
+  vfprintf(stderr, format, ap);
+  va_end(ap);
+}