Change base::Value::ListStorage to std::vector<base::Value>

This CL is a first step to inlining base::ListValue. It is proposed to use an
std::vector<base::Value> as the underlying ListStorage. This CL implements the
change and updates the code accordingly.

TBR=bajones@chromium.org, dbeam@chromium.org, stevenjb@chromium.org
BUG=646113
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2740143002
Cr-Original-Commit-Position: refs/heads/master@{#463618}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ebab0defaea3aed024283a64088ebc0cd352b47f
diff --git a/gaia/gaia_auth_fetcher.cc b/gaia/gaia_auth_fetcher.cc
index 03bd8a4..c5c3f1c 100644
--- a/gaia/gaia_auth_fetcher.cc
+++ b/gaia/gaia_auth_fetcher.cc
@@ -499,7 +499,7 @@
        iter != sessionsList->end();
        iter++) {
     base::DictionaryValue* sessionDictionary;
-    if (!(*iter)->GetAsDictionary(&sessionDictionary))
+    if (!iter->GetAsDictionary(&sessionDictionary))
       continue;
 
     if (sessionDictionary->GetString("login_hint", login_hint))