[url] Reserve output buffer for various URL parsing paths

url/url_canon_relative.cc

Index: url/url_canon_relative.cc
diff --git a/url/url_canon_relative.cc b/url/url_canon_relative.cc
index e34ea2fa2495dc6acbb301644dca4b04b3738762..8259056f5e515320b27479316c561afa8165f61c 100644
--- a/url/url_canon_relative.cc
+++ b/url/url_canon_relative.cc
@@ -4,6 +4,8 @@
 
 // Canonicalizer functions for working with and resolving relative URLs.
 
+#include <algorithm>
+
 #include "base/logging.h"
 #include "url/url_canon.h"
 #include "url/url_canon_internal.h"
@@ -264,7 +266,7 @@ int CopyBaseDriveSpecIfNecessary(const char* base_url,
 #endif  // WIN32
 
 // A subroutine of DoResolveRelativeURL, this resolves the URL knowning that
-// the input is a relative path or less (qyuery or ref).
+// the input is a relative path or less (query or ref).
 template<typename CHAR>
 bool DoResolveRelativePath(const char* base_url,
                            const Parsed& base_parsed,
@@ -280,7 +282,13 @@ bool DoResolveRelativePath(const char* base_url,
   // also know we have a path so can copy up to there.
   Component path, query, ref;
   ParsePathInternal(relative_url, relative_component, &path, &query, &ref);
-  // Canonical URLs always have a path, so we can use that offset.
+
+  // Canonical URLs always have a path, so we can use that offset. Reserve
+  // enough room for the base URL, the new path, and some extra bytes for
+  // possible escaped characters.
+  output->ReserveSizeIfNeeded(
+      base_parsed.path.begin +
+      std::max(path.end(), std::max(query.end(), ref.end())) + 8);
   output->Append(base_url, base_parsed.path.begin);
 
   if (path.len > 0) {
@@ -394,6 +402,11 @@ bool DoResolveRelativeHost(const char* base_url,
   replacements.SetQuery(relative_url, relative_parsed.query);
   replacements.SetRef(relative_url, relative_parsed.ref);
 
+  // Length() does not include the old scheme, so make sure to add it from the
+  // base URL.
+  output->ReserveSizeIfNeeded(
+      replacements.components().Length() +
+      base_parsed.CountCharactersBefore(Parsed::USERNAME, false) + 8);
   return ReplaceStandardURL(base_url, base_parsed, replacements,
                             query_converter, output, out_parsed);
 }