Bug 1431028 - Don't discard the back buffer in ClientSingleTiledLayerBuffer. r=mattwoodrow

MozReview-Commit-ID: HHbqlAnSVmN

gfx/layers/client/SingleTiledContentClient.cpp

@@ -336,12 +336,6 @@ ClientSingleTiledLayerBuffer::PaintThebes(const nsIntRegion& aNewValidRegion,
   mTile.Flip();
   UnlockTile(mTile);
 
-  if (backBuffer->HasIntermediateBuffer()) {
-    // If our new buffer has an internal buffer, we don't want to keep another
-    // TextureClient around unnecessarily, so discard the back-buffer.
-    mTile.DiscardBackBuffer();
-  }
-
   mValidRegion = aNewValidRegion;
   mLastPaintSurfaceMode = mode;
   mLastPaintContentType = content;