Add missing include for sleep().

This used to be leaked unconditionally by libc++.

Change-Id: I984ab7328ff3a2499c3c89a6862feaa62b6166de

Author: Dan Albert<danalbert@google.com>

Cherry-pick of https://android-review.googlesource.com/#/c/178189/1

This fixes the AOSP mips build.

Review URL: https://codereview.chromium.org/1425843003
diff --git a/dm/DM.cpp b/dm/DM.cpp
index f1f54d3..2723103 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -41,6 +41,10 @@
 
 #include <stdlib.h>
 
+#ifndef SK_BUILD_FOR_WIN32
+    #include <unistd.h>
+#endif
+
 DEFINE_string(src, "tests gm skp image", "Source types to test.");
 DEFINE_bool(nameByHash, false,
             "If true, write to FLAGS_writePath[0]/<hash>.png instead of "