[Spellcheck] Switch to https download

Download dictionaries via https instead of http, preventing MITM
attacks against dicts. Plus, HTTPS 4 LYFE!

BUG=479162

Review URL: https://codereview.chromium.org/1056103005

Cr-Commit-Position: refs/heads/master@{#326954}

chrome/browser/spellchecker/spellcheck_hunspell_dictionary.cc

@@ -214,7 +214,7 @@ void SpellcheckHunspellDictionary::OnURLFetchComplete(
 
 GURL SpellcheckHunspellDictionary::GetDictionaryURL() {
   static const char kDownloadServerUrl[] =
-      "http://cache.pack.google.com/edgedl/chrome/dict/";
+      "https://redirector.gvt1.com/edgedl/chrome/dict/";
   std::string bdict_file = dictionary_file_.path.BaseName().MaybeAsASCII();
 
   DCHECK(!bdict_file.empty());