url: Have GURL::Resolve() take StringPiece instead of string const-ref.

This way, callers that have a base::StringPiece[16] can avoid copying
the data into an {std::string, base::String16} just to call
GURL::Resolve().

Change-Id: I0c7d73ac55d102bc0bc39afe36efccc33e938e14
Reviewed-on: https://chromium-review.googlesource.com/1195740Reviewed-by: Chris Palmer <palmer@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587673}

url/gurl.cc

@@ -176,7 +176,7 @@ bool GURL::operator>(const GURL& other) const {
 }
 
 // Note: code duplicated below (it's inconvenient to use a template here).
-GURL GURL::Resolve(const std::string& relative) const {
+GURL GURL::Resolve(base::StringPiece relative) const {
   // Not allowed for invalid URLs.
   if (!is_valid_)
     return GURL();
@@ -202,7 +202,7 @@ GURL GURL::Resolve(const std::string& relative) const {
 }
 
 // Note: code duplicated above (it's inconvenient to use a template here).
-GURL GURL::Resolve(const base::string16& relative) const {
+GURL GURL::Resolve(base::StringPiece16 relative) const {
   // Not allowed for invalid URLs.
   if (!is_valid_)
     return GURL();

url/gurl.h

@@ -151,8 +151,8 @@ class URL_EXPORT GURL {
   //
   // It is an error to resolve a URL relative to an invalid URL. The result
   // will be the empty URL.
-  GURL Resolve(const std::string& relative) const;
-  GURL Resolve(const base::string16& relative) const;
+  GURL Resolve(base::StringPiece relative) const;
+  GURL Resolve(base::StringPiece16 relative) const;
 
   // Creates a new GURL by replacing the current URL's components with the
   // supplied versions. See the Replacements class in url_canon.h for more.