Process Statistics header, add max RSS to render_pdfs

tools/ProcStats.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef ProcStats_DEFINED
+#define ProcStats_DEFINED
+
+/**
+ * ProcStats - Process Statistics Functions
+ */
+
+namespace sk_tools {
+
+/**
+ *  If not implemented for this OS, returns -1.  Otherwise, return
+ *  the maximum resident set size, as reported by getrusage().
+ */
+int getMaxResidentSetSizeKB();
+
+}  // namespace sk_tools
+
+#endif  // ProcStats_DEFINED