[oilpan] Completely move HTMLFormControlElement's hierarchy to the managed heap

Source/core/page/DragController.cpp

Index: Source/core/page/DragController.cpp
diff --git a/Source/core/page/DragController.cpp b/Source/core/page/DragController.cpp
index 16512e01adb2dbf1c2af9d6a7094ca1e894e1b1e..42c5ce8282e3340320b82bfabe94c8cdcef3fd2d 100644
--- a/Source/core/page/DragController.cpp
+++ b/Source/core/page/DragController.cpp
@@ -211,7 +211,7 @@ void DragController::dragExited(DragData* dragData)
     mouseMovedIntoDocument(0);
     if (m_fileInputElementUnderMouse)
         m_fileInputElementUnderMouse->setCanReceiveDroppedFiles(false);
-    m_fileInputElementUnderMouse = 0;
+    m_fileInputElementUnderMouse.clear();
 }
 
 DragSession DragController::dragUpdated(DragData* dragData)
@@ -285,17 +285,17 @@ DragSession DragController::dragEnteredOrUpdated(DragData* dragData)
     return dragSession;
 }
 
-static HTMLInputElement* asFileInput(Node* node)
+static Result<HTMLInputElement> asFileInput(Node* node)
 {
     ASSERT(node);
 
-    HTMLInputElement* inputElement = node->toInputElement();
+    Handle<HTMLInputElement> inputElement = node->toInputElement();
 
     // If this is a button inside of the a file input, move up to the file input.
     if (inputElement && inputElement->isTextButton() && inputElement->treeScope()->rootNode()->isShadowRoot())
         inputElement = toShadowRoot(Handle<Node>(inputElement->treeScope()->rootNode()).raw())->host()->toInputElement();
 
-    return inputElement && inputElement->isFileUpload() ? inputElement : 0;
+    return inputElement && inputElement->isFileUpload() ? inputElement : nullptr;
 }
 
 // This can return null if an empty document is loaded.
@@ -362,7 +362,7 @@ bool DragController::tryDocumentDrag(DragData* dragData, DragDestinationAction a
         if (!element)
             return false;
         
-        HTMLInputElement* elementAsFileInput = asFileInput(element);
+        Handle<HTMLInputElement> elementAsFileInput = asFileInput(element);
         if (m_fileInputElementUnderMouse != elementAsFileInput) {
             if (m_fileInputElementUnderMouse)
                 m_fileInputElementUnderMouse->setCanReceiveDroppedFiles(false);
@@ -404,7 +404,7 @@ bool DragController::tryDocumentDrag(DragData* dragData, DragDestinationAction a
     m_page->dragCaretController()->clear();
     if (m_fileInputElementUnderMouse)
         m_fileInputElementUnderMouse->setCanReceiveDroppedFiles(false);
-    m_fileInputElementUnderMouse = 0;
+    m_fileInputElementUnderMouse.clear();
     return false;
 }
 
@@ -447,10 +447,10 @@ bool DragController::concludeEditDrag(DragData* dragData)
 {
     ASSERT(dragData);
 
-    RefPtr<HTMLInputElement> fileInput = m_fileInputElementUnderMouse;
+    Handle<HTMLInputElement> fileInput = m_fileInputElementUnderMouse;
     if (m_fileInputElementUnderMouse) {
         m_fileInputElementUnderMouse->setCanReceiveDroppedFiles(false);
-        m_fileInputElementUnderMouse = 0;
+        m_fileInputElementUnderMouse.clear();
     }
 
     if (!m_documentUnderMouse)