AU: Timestamp logs at startup.

This will allow logs to be rotated by init/chromeos-cleanup-logs (separate CL).

BUG=5527
TEST=tested on device, chrome://system

Change-Id: I844ebd198510a8f600afa99f840624b2e65d1584

Review URL: http://codereview.chromium.org/4771007
diff --git a/utils.cc b/utils.cc
index 162fe7b..359b6b8 100644
--- a/utils.cc
+++ b/utils.cc
@@ -301,6 +301,11 @@
   return 0 == lstat(path, &stbuf);
 }
 
+bool IsSymlink(const char* path) {
+  struct stat stbuf;
+  return lstat(path, &stbuf) == 0 && S_ISLNK(stbuf.st_mode) != 0;
+}
+
 std::string TempFilename(string path) {
   static const string suffix("XXXXXX");
   CHECK(StringHasSuffix(path, suffix));