Remove IsPointerConvertible trait and hacks and just use std::is_base_of.

third_party/WebKit/Source/platform/JSONValues.h

Index: third_party/WebKit/Source/platform/JSONValues.h
diff --git a/third_party/WebKit/Source/platform/JSONValues.h b/third_party/WebKit/Source/platform/JSONValues.h
index aa882151aa3d1fa79bd646af40949ffa8aa1d1ef..bdb9d2d6880293d91fff51fe1f8bd8c964699ab4 100644
--- a/third_party/WebKit/Source/platform/JSONValues.h
+++ b/third_party/WebKit/Source/platform/JSONValues.h
@@ -47,32 +47,6 @@ class JSONValue;
 
 } // namespace blink
 
-namespace WTF {
-
-class StringBuilder;
-
-// FIXME: Avoid the need for this global upcasting to JSONValue (for PassRefPtr<T>.)
-// The current CodeGeneratorInspector.py generates code which order sorts its input
-// types and generates forward declarations where needed. But with inline uses
-// of setValue(PassRefPtr<JSONValue>) this is not quite sufficient for the
-// implicit conversion of PassRefPtr<T> to PassRefPtr<JSONValue> for a T that
-// has only been forward declared -- IsPointerConvertible<> doesn't have
-// complete types to work with.
-//
-// Work around that problem here by hackily declaring this global & unsafe
-// specialization.
-//
-// (InspectorTypeBuilder.h is the only piece of code that relies on this specialization.)
-template<typename From> class IsPointerConvertible<From, blink::JSONValue> {
-    STATIC_ONLY(IsPointerConvertible);
-public:
-    enum {
-        Value = true
-    };
-};
-
-} // namespace WTF
-
 namespace blink {
 
 class JSONArray;