Add support for IsGarbageCollectedType<void>

Currently IsGarbageCollectedType<void> and PointerParamStorageTraits<void*> can't be compiled.
This CL makes them successfully compiled, and removes ParamStorageTraits<void*> specialization.

BUG=597856

Review-Url: https://codereview.chromium.org/1923183002
Cr-Commit-Position: refs/heads/master@{#390331}

third_party/WebKit/Source/platform/heap/GarbageCollected.h

@@ -99,6 +99,11 @@ struct IsGarbageCollectedType {
         || isHeapAllocatedListHashSetNode;
 };
 
+template <>
+struct IsGarbageCollectedType<void> {
+    static const bool value = false;
+};
+
 // The GarbageCollectedMixin interface and helper macro
 // USING_GARBAGE_COLLECTED_MIXIN can be used to automatically define
 // TraceTrait/ObjectAliveTrait on non-leftmost deriving classes

third_party/WebKit/Source/platform/heap/Handle.h

@@ -1159,10 +1159,11 @@ template<typename T> inline T* getPtr(const blink::Persistent<T>& p)
 // For wtf/Functional.h
 template<typename T, bool isGarbageCollected> struct PointerParamStorageTraits;
 
+// The condition of 'T must be fully defined' (except for void) is checked in
+// blink::IsGarbageCollectedType<T>::value.
 template<typename T>
 struct PointerParamStorageTraits<T*, false> {
     STATIC_ONLY(PointerParamStorageTraits);
-    static_assert(sizeof(T), "T must be fully defined");
     using StorageType = T*;
 
     static StorageType wrap(T* value) { return value; }
@@ -1172,7 +1173,6 @@ struct PointerParamStorageTraits<T*, false> {
 template<typename T>
 struct PointerParamStorageTraits<T*, true> {
     STATIC_ONLY(PointerParamStorageTraits);
-    static_assert(sizeof(T), "T must be fully defined");
     using StorageType = blink::CrossThreadPersistent<T>;
 
     static StorageType wrap(T* value) { return value; }
@@ -1182,7 +1182,6 @@ struct PointerParamStorageTraits<T*, true> {
 template<typename T>
 struct ParamStorageTraits<T*> : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
     STATIC_ONLY(ParamStorageTraits);
-    static_assert(sizeof(T), "T must be fully defined");
 };
 
 template<typename T>

third_party/WebKit/Source/wtf/Functional.h

@@ -214,14 +214,6 @@ struct ParamStorageTraits<RetainPtr<T>> {
     static typename RetainPtr<T>::PtrType unwrap(const StorageType& value) { return value.get(); }
 };
 
-template <>
-struct ParamStorageTraits<void*> {
-    typedef void* StorageType;
-
-    static StorageType wrap(void* value) { return value; }
-    static void* unwrap(const StorageType& value) { return value; }
-};
-
 template <typename T>
 struct ParamStorageTraits<PassedWrapper<T>> {
     typedef PassedWrapper<T> StorageType;