Enable building pdf_use_skia in the standalone build.

skia/skia_pdfium.gypi

+# Copyright 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.
+
+
+# This gypi file contains all the Chrome-specific enhancements to Skia.
+# In component mode (shared_lib) it is folded into a single shared library with
+# the Skia files but in all other cases it is a separate library.
+{
+  'dependencies': [
+    'skia_library',
+  ],
+
+  'direct_dependent_settings': {
+    'include_dirs': [
+      'ext',
+    ],
+  },
+  'variables': {
+    # TODO(scottmg): http://crbug.com/177306
+    'clang_warning_flags_unset': [
+      # Don't warn about string->bool used in asserts.
+      '-Wstring-conversion',
+    ],
+  },
+  'sources': [
+    'ext/google_logging.cc',
+  ],
+}