Change other usages of .size() to .empty() when applicable.

chrome/browser/download/download_util.cc

Index: chrome/browser/download/download_util.cc
diff --git a/chrome/browser/download/download_util.cc b/chrome/browser/download/download_util.cc
index 69dcce6c74af8b2d854cc7e9de1bba0f748c886c..e0bc5070b26ed470a0fb0480dfe504a6230ffb92 100644
--- a/chrome/browser/download/download_util.cc
+++ b/chrome/browser/download/download_util.cc
@@ -113,8 +113,8 @@ bool IsShellIntegratedExtension(const string16& extension) {
   // See <http://www.juniper.net/security/auto/vulnerabilities/vuln2612.html>.
   // That vulnerability report is not exactly on point, but files become magical
   // if their end in a CLSID.  Here we block extensions that look like CLSIDs.
-  if (extension_lower.size() > 0 && extension_lower.at(0) == L'{' &&
-      extension_lower.at(extension_lower.length() - 1) == L'}')
+  if (!extension_lower.empty() && extension_lower[0] == L'{' &&
+      extension_lower[extension_lower.length() - 1] == L'}')
     return true;
 
   return false;