Bug 1347646 Part 2: Use CreateRenderingContext in nsSimplePageSequenceFrame::PrePrintNextPage to ensure recorder is used for canvases. r=jwatt

Calling CreateReferenceRenderingContext currently returns a non-recording DrawTarget even
when the nsIDeviceContextSpec within the nsDeviceContext has a DrawEventRecorder, due to
bug 1354624. Since we've already called BeginPage we can call CreateRenderingContext instead
though and that will give us a recording DrawTarget as we require to record the canvas drawing.

layout/generic/nsSimplePageSequenceFrame.cpp

@@ -629,7 +629,7 @@ nsSimplePageSequenceFrame::PrePrintNextPage(nsITimerCallback* aCallback, bool* a
 
       mCalledBeginPage = true;
       
-      RefPtr<gfxContext> renderingContext = dc->CreateReferenceRenderingContext();
+      RefPtr<gfxContext> renderingContext = dc->CreateRenderingContext();
       NS_ENSURE_TRUE(renderingContext, NS_ERROR_OUT_OF_MEMORY);
 
       DrawTarget* drawTarget = renderingContext->GetDrawTarget();