Bug 1649121: part 88) Declare some methods around `DataTransfer` `const`. r=masayuki

Helps reasoning about them.

Differential Revision: https://phabricator.services.mozilla.com/D90528

dom/events/DataTransfer.cpp

@@ -336,7 +336,8 @@ bool DataTransfer::HasType(const nsAString& aType) const {
 bool DataTransfer::HasFile() const { return mItems->HasFile(); }
 
 void DataTransfer::GetData(const nsAString& aFormat, nsAString& aData,
-                           nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+                           nsIPrincipal& aSubjectPrincipal,
+                           ErrorResult& aRv) const {
   // return an empty string if data for the format was not found
   aData.Truncate();
 
@@ -481,7 +482,7 @@ already_AddRefed<DOMStringList> DataTransfer::MozTypesAt(
 
 nsresult DataTransfer::GetDataAtNoSecurityCheck(const nsAString& aFormat,
                                                 uint32_t aIndex,
-                                                nsIVariant** aData) {
+                                                nsIVariant** aData) const {
   return GetDataAtInternal(aFormat, aIndex,
                            nsContentUtils::GetSystemPrincipal(), aData);
 }
@@ -489,7 +490,7 @@ nsresult DataTransfer::GetDataAtNoSecurityCheck(const nsAString& aFormat,
 nsresult DataTransfer::GetDataAtInternal(const nsAString& aFormat,
                                          uint32_t aIndex,
                                          nsIPrincipal* aSubjectPrincipal,
-                                         nsIVariant** aData) {
+                                         nsIVariant** aData) const {
   *aData = nullptr;
 
   if (aFormat.IsEmpty()) {

dom/events/DataTransfer.h

@@ -202,7 +202,7 @@ class DataTransfer final : public nsISupports, public nsWrapperCache {
   bool HasFile() const;
 
   void GetData(const nsAString& aFormat, nsAString& aData,
-               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv);
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) const;
 
   void SetData(const nsAString& aFormat, const nsAString& aData,
                nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv);
@@ -281,7 +281,7 @@ class DataTransfer final : public nsISupports, public nsWrapperCache {
   mozilla::dom::Element* GetDragTarget() const { return mDragTarget; }
 
   nsresult GetDataAtNoSecurityCheck(const nsAString& aFormat, uint32_t aIndex,
-                                    nsIVariant** aData);
+                                    nsIVariant** aData) const;
 
   DataTransferItemList* Items() const { return mItems; }
 
@@ -421,7 +421,7 @@ class DataTransfer final : public nsISupports, public nsWrapperCache {
   FileList* GetFilesInternal(ErrorResult& aRv, nsIPrincipal* aSubjectPrincipal);
   nsresult GetDataAtInternal(const nsAString& aFormat, uint32_t aIndex,
                              nsIPrincipal* aSubjectPrincipal,
-                             nsIVariant** aData);
+                             nsIVariant** aData) const;
 
   nsresult SetDataAtInternal(const nsAString& aFormat, nsIVariant* aData,
                              uint32_t aIndex, nsIPrincipal* aSubjectPrincipal);

editor/libeditor/HTMLEditor.h

@@ -4172,9 +4172,10 @@ class HTMLEditor final : public TextEditor,
    * InsertFromDataTransfer() is called only when user drops data into
    * this editor.  Don't use this method for other purposes.
    */
-  MOZ_CAN_RUN_SCRIPT nsresult InsertFromDataTransfer(
+  MOZ_CAN_RUN_SCRIPT nsresult
-      dom::DataTransfer* aDataTransfer, int32_t aIndex, Document* aSourceDoc,
+  InsertFromDataTransfer(const dom::DataTransfer* aDataTransfer, int32_t aIndex,
-      const EditorDOMPoint& aDroppedAt, bool aDoDeleteSelection);
+                         Document* aSourceDoc, const EditorDOMPoint& aDroppedAt,
+                         bool aDoDeleteSelection);
 
   bool HavePrivateHTMLFlavor(nsIClipboard* clipboard);
 

editor/libeditor/HTMLEditorDataTransfer.cpp

@@ -1771,7 +1771,7 @@ nsresult HTMLEditor::InsertFromTransferable(nsITransferable* aTransferable,
   return NS_OK;
 }
 
-static void GetStringFromDataTransfer(DataTransfer* aDataTransfer,
+static void GetStringFromDataTransfer(const DataTransfer* aDataTransfer,
                                       const nsAString& aType, int32_t aIndex,
                                       nsString& aOutputString) {
   nsCOMPtr<nsIVariant> variant;
@@ -1788,7 +1788,7 @@ static void GetStringFromDataTransfer(DataTransfer* aDataTransfer,
   nsContentUtils::PlatformToDOMLineBreaks(aOutputString);
 }
 
-nsresult HTMLEditor::InsertFromDataTransfer(DataTransfer* aDataTransfer,
+nsresult HTMLEditor::InsertFromDataTransfer(const DataTransfer* aDataTransfer,
                                             int32_t aIndex,
                                             Document* aSourceDoc,
                                             const EditorDOMPoint& aDroppedAt,