Bug 946475 - Add unit test for ClearRect where the cleared area doesn't cover all of the clip. r=Bas
Bug 946475 - Clip to the clear area in DrawTargetD2D::ClearRect so that we don't accidentally restore pixels that weren't drawn. r=Bas
Bug 946475 - Avoid using AutoSaveRestoreClippedOut for ClearRect when the cumulative clip can be represented as a single axis aligned rectangle. r=Bas