Make ExtensionIconSet::ContainsPath use StringPiece.

extensions/browser/extension_protocols.cc

Index: extensions/browser/extension_protocols.cc
diff --git a/extensions/browser/extension_protocols.cc b/extensions/browser/extension_protocols.cc
index a9164ea76ccb5852969b694f6f8cb48d63dd81bf..43b6dbbf7fdfed20226ec3c949e4547318e71f21 100644
--- a/extensions/browser/extension_protocols.cc
+++ b/extensions/browser/extension_protocols.cc
@@ -393,11 +393,12 @@ bool URLIsForExtensionIcon(const GURL& url, const Extension* extension) {
   if (!extension)
     return false;
 
-  std::string path = url.path();
   DCHECK_EQ(url.host(), extension->id());
+  base::StringPiece path = url.path_piece();
   DCHECK(path.length() > 0 && path[0] == '/');
-  path = path.substr(1);
-  return extensions::IconsInfo::GetIcons(extension).ContainsPath(path);
+  base::StringPiece path_without_slash = path.substr(1);
+  return extensions::IconsInfo::GetIcons(extension).ContainsPath(
+      path_without_slash);
 }
 
 class ExtensionProtocolHandler