Move FontResourceClient to Oilpan heap

This change makes FontResourceClient a GarbageCollectedMixin
subclass.

Registering a prefinalizer in a class T is not possible when
 - T has multiple GarbageCollectedMixin base classes, and
 - T doesn't have USING_GARBAGE_COLLECTED_MIXIN statement.

Hence this CL modifies ResourceOwner<R, C> definition so that it
inherits GarbageCollectedMixin only when C is not derived from
GarbageCollectedMixin.

BUG=587663

Review-Url: https://codereview.chromium.org/2014533002
Cr-Commit-Position: refs/heads/master@{#397045}

third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp

@@ -219,6 +219,7 @@ DEFINE_TRACE(RemoteFontFaceSource)
     visitor->trace(m_font);
     visitor->trace(m_fontSelector);
     CSSFontFaceSource::trace(visitor);
+    FontResourceClient::trace(visitor);
 }
 
 void RemoteFontFaceSource::FontLoadHistograms::loadStarted()

third_party/WebKit/Source/core/css/RemoteFontFaceSource.h

@@ -24,6 +24,7 @@ enum FontDisplay {
 
 class RemoteFontFaceSource final : public CSSFontFaceSource, public FontResourceClient {
     USING_PRE_FINALIZER(RemoteFontFaceSource, dispose);
+    USING_GARBAGE_COLLECTED_MIXIN(RemoteFontFaceSource);
 public:
     enum DisplayPeriod { BlockPeriod, SwapPeriod, FailurePeriod };
 

third_party/WebKit/Source/core/fetch/FontResource.h

@@ -30,6 +30,7 @@
 #include "core/fetch/ResourceClient.h"
 #include "platform/Timer.h"
 #include "platform/fonts/FontOrientation.h"
+#include "platform/heap/Handle.h"
 #include "wtf/OwnPtr.h"
 
 namespace blink {
@@ -95,13 +96,15 @@ private:
 
 DEFINE_RESOURCE_TYPE_CASTS(Font);
 
-class FontResourceClient : public ResourceClient {
+class FontResourceClient : public GarbageCollectedMixin, public ResourceClient {
 public:
     ~FontResourceClient() override {}
     static bool isExpectedType(ResourceClient* client) { return client->getResourceClientType() == FontType; }
     ResourceClientType getResourceClientType() const final { return FontType; }
     virtual void fontLoadShortLimitExceeded(FontResource*) {}
     virtual void fontLoadLongLimitExceeded(FontResource*) {}
+
+    DEFINE_INLINE_VIRTUAL_TRACE() {}
 };
 
 } // namespace blink

third_party/WebKit/Source/core/fetch/ResourceOwner.h

@@ -32,22 +32,49 @@
 #define ResourceOwner_h
 
 #include "core/fetch/Resource.h"
+#include <type_traits>
 
 namespace blink {
 
+template <typename Client, bool isClientGarbageCollectedMixin>
+class ResourceOwnerBase;
+
+template <typename Client>
+class ResourceOwnerBase<Client, true> : public Client {
+public:
+    DEFINE_INLINE_VIRTUAL_TRACE()
+    {
+        Client::trace(visitor);
+    }
+};
+
+// TODO(yhirano): Remove this template once all ResourceClients become
+// GarbageCollectedMixin.
+template <typename Client>
+class ResourceOwnerBase<Client, false> : public GarbageCollectedMixin, public Client {
+public:
+    DEFINE_INLINE_VIRTUAL_TRACE() {}
+};
+
 template<class R, class C = typename R::ClientType>
-class ResourceOwner : public GarbageCollectedMixin, public C {
+class ResourceOwner : public ResourceOwnerBase<C, std::is_base_of<GarbageCollectedMixin, C>::value> {
     USING_PRE_FINALIZER(ResourceOwner, clearResource);
 public:
     using ResourceType = R;
+    ~ResourceOwner() override {}
+    ResourceType* resource() const { return m_resource; }
 
-    virtual ~ResourceOwner();
-    ResourceType* resource() const { return m_resource.get(); }
-
-    DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(m_resource); }
+    DEFINE_INLINE_TRACE()
+    {
+        visitor->trace(m_resource);
+        ResourceOwnerBase<C, std::is_base_of<GarbageCollectedMixin, C>::value>::trace(visitor);
+    }
 
 protected:
-    ResourceOwner();
+    ResourceOwner()
+    {
+        ThreadState::current()->registerPreFinalizer(this);
+    }
 
     void setResource(ResourceType*);
     void clearResource() { setResource(nullptr); }
@@ -56,17 +83,6 @@ private:
     Member<ResourceType> m_resource;
 };
 
-template<class R, class C>
-inline ResourceOwner<R, C>::ResourceOwner()
-{
-    ThreadState::current()->registerPreFinalizer(this);
-}
-
-template<class R, class C>
-inline ResourceOwner<R, C>::~ResourceOwner()
-{
-}
-
 template<class R, class C>
 inline void ResourceOwner<R, C>::setResource(R* newResource)
 {