Add scoped_ptr-safe base::Value to Dictionary/List conversion functions.

base/values.h

Index: base/values.h
diff --git a/base/values.h b/base/values.h
index 8756debdbdf76a0dc9658af0ec6c14159885f905..56be542d7477b8c02d725aa7690e1b82dacc70d3 100644
--- a/base/values.h
+++ b/base/values.h
@@ -209,6 +209,9 @@ class BASE_EXPORT BinaryValue: public Value {
 // are |std::string|s and should be UTF-8 encoded.
 class BASE_EXPORT DictionaryValue : public Value {
  public:
+  // Returns |value| if it is a dictionary, nullptr otherwise.
+  static scoped_ptr<DictionaryValue> From(scoped_ptr<Value> value);
+
   DictionaryValue();
   ~DictionaryValue() override;
 
@@ -387,6 +390,9 @@ class BASE_EXPORT ListValue : public Value {
   typedef ValueVector::iterator iterator;
   typedef ValueVector::const_iterator const_iterator;
 
+  // Returns |value| if it is a list, nullptr otherwise.
+  static scoped_ptr<ListValue> From(scoped_ptr<Value> value);
+
   ListValue();
   ~ListValue() override;