Make base::Value::TYPE a scoped enum.

As mentioned in the base::Value refactor proposal, base::Value::Type should be a
C++11 style scoped enumeration. This change addresses this issue by adding the
required keyword, making the necessary substitutions and adding casts where
needed.

[email protected]
BUG=646113
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2539363004
Cr-Commit-Position: refs/heads/master@{#436961}
diff --git a/extensions/utility/unpacker.cc b/extensions/utility/unpacker.cc
index 3620f388..cec0db8 100644
--- a/extensions/utility/unpacker.cc
+++ b/extensions/utility/unpacker.cc
@@ -164,7 +164,7 @@
     return nullptr;
   }
 
-  if (!root->IsType(base::Value::TYPE_DICTIONARY)) {
+  if (!root->IsType(base::Value::Type::DICTIONARY)) {
     *error = errors::kInvalidManifest;
     return nullptr;
   }