Add missing unistd.h include after r8765.

TEST=Build with GCC 4.8.0 and glibc 2.17.
R=reed@google.com, jvanverth@google.com, bsalomon@google.com

Author: raphael.kubo.da.costa@intel.com

Review URL: https://chromiumcodereview.appspot.com/14401007

git-svn-id: http://skia.googlecode.com/svn/trunk@8809 2bbb7eff-a529-9590-31e7-b0007b416f81

src/ports/SkFontHost_fontconfig.cpp

@@ -237,6 +237,7 @@ static bool is_lower(char c) {
 
 #include "SkFontMgr.h"
 #include <fontconfig/fontconfig.h>
+#include <unistd.h>
 
 static int get_int(FcPattern* pattern, const char field[]) {
     int value;