Bug 323088 - RGB values slightly off in canvas after drawWindow().
Use a table indexed by bit depth to provide a better "scale factor" when
copying pixels from native surfaces to the canvas.
Patch by roc, r=vladimir, sr=shaver, a=dveditz.
git-svn-id: svn://10.0.0.236/branches/MOZILLA_1_8_0_BRANCH@193470 18797224-902f-48f8-a5cc-f745e15eee43