[DOM] Update some DOM canvas checks.

dom/canvas/CanvasRenderingContext2D.cpp

@@ -4356,6 +4356,9 @@ CanvasRenderingContext2D::DrawOrMeasureText(const nsAString& aRawText,
     textToDraw.Truncate();
   }
 
+  // This is only needed to know if we can know the drawing bounding box easily.
+  const bool doCalculateBounds = NeedToCalculateBounds();
+  
   // for now, default to ltr if not in doc
   bool isRTL = false;
 
@@ -4376,8 +4379,6 @@ CanvasRenderingContext2D::DrawOrMeasureText(const nsAString& aRawText,
     isRTL = GET_BIDI_OPTION_DIRECTION(document->GetBidiOptions()) == IBMBIDI_TEXTDIRECTION_RTL;
   }
 
-  // This is only needed to know if we can know the drawing bounding box easily.
-  const bool doCalculateBounds = NeedToCalculateBounds();
   if (presShell->IsDestroying()) {
     return NS_ERROR_FAILURE;
   }

dom/canvas/CanvasRenderingContext2D.h

@@ -890,7 +890,9 @@ protected:
    * last call to UpdateFilter and now.
    */
   const gfx::FilterDescription& EnsureUpdatedFilter() {
-    bool isWriteOnly = mCanvasElement && mCanvasElement->IsWriteOnly();
+    bool isWriteOnly = IsWriteOnly() ||
+                       (mCanvasElement && mCanvasElement->IsWriteOnly()) ||
+                       (mOffscreenCanvas && mOffscreenCanvas->IsWriteOnly());
     if (CurrentState().filterSourceGraphicTainted != isWriteOnly) {
       UpdateFilter();
       EnsureTarget();