Avoid parsing the webstore base url so much.

chrome/common/extensions/chrome_extensions_client.h

Index: chrome/common/extensions/chrome_extensions_client.h
diff --git a/chrome/common/extensions/chrome_extensions_client.h b/chrome/common/extensions/chrome_extensions_client.h
index 87b8f828f74d52fdddc6e40ea55ae430397825eb..0610aee2f777021346349a150e9d22d8b59f26f5 100644
--- a/chrome/common/extensions/chrome_extensions_client.h
+++ b/chrome/common/extensions/chrome_extensions_client.h
@@ -47,7 +47,7 @@ class ChromeExtensionsClient : public ExtensionsClient {
   base::StringPiece GetAPISchema(const std::string& name) const override;
   bool ShouldSuppressFatalErrors() const override;
   void RecordDidSuppressFatalError() override;
-  std::string GetWebstoreBaseURL() const override;
+  const GURL& GetWebstoreBaseURL() const override;
   const GURL& GetWebstoreUpdateURL() const override;
   bool IsBlacklistUpdateURL(const GURL& url) const override;
   std::set<base::FilePath> GetBrowserImagePaths(
@@ -69,6 +69,7 @@ class ChromeExtensionsClient : public ExtensionsClient {
   ScriptingWhitelist scripting_whitelist_;
 
   // Mutable to allow caching in a const method.
+  mutable GURL webstore_base_url_;
   mutable GURL webstore_update_url_;
 
   friend struct base::DefaultLazyInstanceTraits<ChromeExtensionsClient>;