Select the polys shown and extrude them imwards a small distance. Detach the selected polys and move them forward, out of the mirror.
In the detached polys, select the edges shown in green and shift-drag them to create the thin line of polys shown in red. Chamfer the green edges to get a nice, sharp edge. The mirror glass in now done, move it back into the mirror casing.
Select the edges shown in red and chamfer them by 0.2. Select the green edges all around the back of the mirror and use the "Connect" tool to create an edge loop about half way down those edges. Select the new edge loop and move it outwards a little to give the back of the mirror a little bit of a bulge.
Create a cylinder and line it up with the edge ring on the back of the mirror.
Extrude the back poly of the cylinder to create the arm of the mirror as shown. You can use a spline to do it if you like. Adjust vertieces to get the shape shown after you extrude. You can unhide the door so that you can make sure that the arm sits on the door properly. Chamfer the edges shown in blue at either end of the arm. Try different chamfer settings till you have something you like. Now just group the mirror with the door and mirror one to the other side of the car and group it with that door.