Fix surface frame size reporting.

The SurfaceHolder provided by the wallpaper service was not reporting
the correct size in getSurfaceFrame().  This broke an optimization in
the ImageWallpaper.  The old code happened to work because calling
lockCanvas on the SurfaceHolder with a null dirty rectangle happened
to have the side-effect of updating the SurfaceHolder's surface frame
size field because it passed mSurfaceFrame as the dirty rect, causing
mSurfaceFrame to be set to the size of the region to be drawn.

However, relying on this side-effect is wrong.  Among other things,
the dirty region could actually be smaller than the surface frame.

This patch fixes WallpaperService, SurfaceView and ViewRoot to ensure
that the surface frame size is always set explicitly and is not modified
by calls to lockCanvas.

Change-Id: I10948f5ec269409ceaf0f7d32b3f6731e9499ebc