base: Add three helper functions to Values API.

base/values.h

Index: base/values.h
diff --git a/base/values.h b/base/values.h
index a30791bc6357c671f56c02c0c39e61027c11aabb..8654b07ba7bb123dcabf551d04df80bae9eb9faf 100644
--- a/base/values.h
+++ b/base/values.h
@@ -70,7 +70,6 @@ class BASE_EXPORT Value {
   // Convenience methods for creating Value objects for various
   // kinds of values without thinking about which class implements them.
   // These can always be expected to return a valid Value*.
-  static Value* CreateNullValue();
   static FundamentalValue* CreateBooleanValue(bool in_value);
   static FundamentalValue* CreateIntegerValue(int in_value);
   static FundamentalValue* CreateDoubleValue(double in_value);
@@ -110,7 +109,7 @@ class BASE_EXPORT Value {
   virtual bool Equals(const Value* other) const;
 
   // Compares if two Value objects have equal contents. Can handle NULLs.
-  // NULLs are considered equal but different from Value::CreateNullValue().
+  // NULLs are considered equal but different from NullValue().
   static bool Equals(const Value* a, const Value* b);
 
  protected:
@@ -126,7 +125,14 @@ class BASE_EXPORT Value {
   DISALLOW_COPY_AND_ASSIGN(Value);
 };
 
-// FundamentalValue represents the simple fundamental types of values.
+// Helper functions. Use TrueValue() and FalseValue() instead of:
+// new FundamentalValue() and CreateBooleanValue().
+BASE_EXPORT Value* NullValue();
+BASE_EXPORT FundamentalValue* TrueValue();
+BASE_EXPORT FundamentalValue* FalseValue();
+
+// FundamentalValue represents one of the fundamental values:
+// bool, int or double.
 class BASE_EXPORT FundamentalValue : public Value {
  public:
   explicit FundamentalValue(bool in_value);
@@ -446,7 +452,7 @@ class BASE_EXPORT ListValue : public Value {
 // deserialize Value objects.
 class BASE_EXPORT ValueSerializer {
  public:
-  virtual ~ValueSerializer();
+  virtual ~ValueSerializer() {}
 
   virtual bool Serialize(const Value& root) = 0;