Bug 1352882 - Part 1. Add releasing nsIDocument option to recycle nsIDocumentEncoder. r=smaug

Editor uses weak reference for nsIDocument.  But nsDocumentEncoder has strong reference of nsIDocument. So to recycle nsIDocumentEncoder, editor wants the option that nsIDocumentEncoder releases nsIDocument into nsDocumentEncoder after EncodeTo* is called.

MozReview-Commit-ID: K3E9XhgD8FY

--HG--
extra : rebase_source : d37983705d574a2443c8f7504c7f5e3f35470ef1

dom/base/nsDocumentEncoder.cpp

@@ -142,6 +142,25 @@ protected:
 
   virtual bool IncludeInContext(nsINode *aNode);
 
+  class MOZ_STACK_CLASS AutoReleaseDocumentIfNeeded final
+  {
+  public:
+    explicit AutoReleaseDocumentIfNeeded(nsDocumentEncoder* aEncoder)
+      : mEncoder(aEncoder)
+    {
+    }
+
+    ~AutoReleaseDocumentIfNeeded()
+    {
+      if (mEncoder->mFlags & RequiresReinitAfterOutput) {
+        mEncoder->mDocument = nullptr;
+      }
+    }
+
+  private:
+    nsDocumentEncoder* mEncoder;
+  };
+
   nsCOMPtr<nsIDocument>          mDocument;
   nsCOMPtr<nsISelection>         mSelection;
   RefPtr<nsRange>              mRange;
@@ -1009,6 +1028,8 @@ nsDocumentEncoder::EncodeToStringWithMaxLength(uint32_t aMaxLength,
   if (!mDocument)
     return NS_ERROR_NOT_INITIALIZED;
 
+  AutoReleaseDocumentIfNeeded autoReleaseDocument(this);
+
   aOutputString.Truncate();
 
   nsString output;

dom/base/nsIDocumentEncoder.idl

@@ -247,6 +247,13 @@ interface nsIDocumentEncoder : nsISupports
    */
   const unsigned long OutputDisallowLineBreaking = (1 << 27);
 
+  /**
+   * Release reference of nsIDocument after using encodeTo* method to recycle
+   * this encoder without holding nsIDocument. To use this encoder again,
+   * we have to call init again.
+   */
+  const unsigned long RequiresReinitAfterOutput = (1 << 28);
+
   /**
    * Initialize with a pointer to the document and the mime type.
    * @param aDocument Document to encode.