Fix localstorage data migration.

content/browser/dom_storage/local_storage_context_mojo.cc

Index: content/browser/dom_storage/local_storage_context_mojo.cc
diff --git a/content/browser/dom_storage/local_storage_context_mojo.cc b/content/browser/dom_storage/local_storage_context_mojo.cc
index 6cc0c76f6b6e2d9ff749ead7c50cbf3e5b2092b0..44a8873178cb7e70a89ab85bdfd5bd772a68ca5b 100644
--- a/content/browser/dom_storage/local_storage_context_mojo.cc
+++ b/content/browser/dom_storage/local_storage_context_mojo.cc
@@ -70,7 +70,11 @@ void NoOpSuccess(bool success) {}
 
 std::vector<uint8_t> String16ToUint8Vector(const base::string16& input) {
   const uint8_t* data = reinterpret_cast<const uint8_t*>(input.data());
-  return std::vector<uint8_t>(data, data + input.size() * sizeof(base::char16));
+  std::vector<uint8_t> result;
+  result.reserve(input.size() * sizeof(base::char16) + 1);
+  result.push_back(0);

[michaeln, 2017/03/22 23:49:51]

The magic "0" value here is pretty magical, it might be worth sharing a function
or a symbol for the value somewhere in common\dom_storage, or short of that,
even duplicating the enum class here. I see the test would pick up a failure in
a future format change, but some breadcrumbs (or compiler errors) might help
more quickly.

[Marijn Kruisselbrink, 2017/03/31 23:06:14]

Yeah, I agree that this isn't very nice. I changed it to at least give the
number a name. Moving to common/dom_storage is something I'd rather not do, as
ultimately the renderer side code should move into blink, so wouldn't be able to
use content/common anyway.

+  result.insert(result.end(), data, data + input.size() * sizeof(base::char16));
+  return result;
 }
 
 void MigrateStorageHelper(