KWin crashes on several situations using Steam, e.g. like running Steam videos on fullscreen or just starting Company of Heroes 2.

Reproducible: Always

Steps to Reproduce:
1. Open steam.
2. Start Company of Heroes 2
3. A warning notification of the game appears that AMD drivers are unsupported
4. Kwin crashes

Actual Results:  
Kwin crashes and all window bars disappear.

Expected Results:  
Nothing should happen

Restarting kwin_x11 and reproduce the steps produce the following terminal output:

kwin_x11
QXcbConnection: XCB error: 3 (BadWindow), sequence: 178, resource id: 37748742, major code: 20 (GetProperty), minor code: 0
OpenGL vendor string:                   X.Org
OpenGL renderer string:                 Gallium 0.4 on AMD PITCAIRN (DRM 2.45.0 / 4.7.4-1-ARCH, LLVM 3.8.1)
OpenGL version string:                  4.1 (Core Profile) Mesa 12.0.3
OpenGL shading language version string: 4.10
Driver:                                 Unknown
GPU class:                              Unknown
OpenGL version:                         4.1
GLSL version:                           4.10
Mesa version:                           12.0.3
X server version:                       1.18.4
Linux kernel version:                   4.7.4
Requires strict binding:                yes
GLSL shaders:                           yes
Texture NPOT support:                   yes
Virtual Machine:                        no
QXcbConnection: XCB error: 9 (BadDrawable), sequence: 2087, resource id: 0, major code: 14 (GetGeometry), minor code: 0
QXcbConnection: XCB error: 9 (BadDrawable), sequence: 2097, resource id: 0, major code: 14 (GetGeometry), minor code: 0                                                                                     
QXcbConnection: XCB error: 9 (BadDrawable), sequence: 2098, resource id: 0, major code: 14 (GetGeometry), minor code: 0                                                                                     
QXcbConnection: XCB error: 9 (BadDrawable), sequence: 2099, resource id: 0, major code: 14 (GetGeometry), minor code: 0                                                                                     
QXcbConnection: XCB error: 9 (BadDrawable), sequence: 2100, resource id: 0, major code: 14 (GetGeometry), minor code: 0                                                                                     
QMetaProperty::read: Unable to handle unregistered datatype 'KWayland::Server::SurfaceInterface*' for property 'KWin::Toplevel::surface'                                                                    
QXcbConnection: XCB error: 3 (BadWindow), sequence: 9890, resource id: 37748759, major code: 18 (ChangeProperty), minor code: 0                                                                             
QXcbConnection: XCB error: 3 (BadWindow), sequence: 9938, resource id: 35652084, major code: 18 (ChangeProperty), minor code: 0                                                                             
QXcbConnection: XCB error: 3 (BadWindow), sequence: 19193, resource id: 81792432, major code: 20 (GetProperty), minor code: 0                                                                               
QXcbConnection: XCB error: 3 (BadWindow), sequence: 35080, resource id: 37748743, major code: 15 (QueryTree), minor code: 0                                                                                 
QXcbConnection: XCB error: 3 (BadWindow), sequence: 35155, resource id: 35652093, major code: 18 (ChangeProperty), minor code: 0                                                                            
QXcbConnection: XCB error: 3 (BadWindow), sequence: 35621, resource id: 81795434, major code: 20 (GetProperty), minor code: 0                                                                               
QXcbConnection: XCB error: 3 (BadWindow), sequence: 36788, resource id: 81795581, major code: 20 (GetProperty), minor code: 0                                                                               
QXcbConnection: XCB error: 3 (BadWindow), sequence: 42552, resource id: 37748743, major code: 15 (QueryTree), minor code: 0                                                                                 
QXcbConnection: XCB error: 3 (BadWindow), sequence: 42624, resource id: 35652099, major code: 18 (ChangeProperty), minor code: 0                                                                            
QXcbConnection: XCB error: 3 (BadWindow), sequence: 44778, resource id: 35652101, major code: 42 (SetInputFocus), minor code: 0                                                                             
QXcbConnection: XCB error: 3 (BadWindow), sequence: 44779, resource id: 35652101, major code: 25 (SendEvent), minor code: 0                                                                                 
QXcbConnection: XCB error: 3 (BadWindow), sequence: 44781, resource id: 35652101, major code: 15 (QueryTree), minor code: 0                                                                                 
QXcbConnection: XCB error: 8 (BadMatch), sequence: 54049, resource id: 16777482, major code: 42 (SetInputFocus), minor code: 0                                                                              
kwin_x11: Couldn't find current GLX or EGL context.                                                                                                                                                      
                                                                                                                                                                                                            
Application::crashHandler() called with signal 11; recent crashes: 1                                                                                                                                        
KCrash: Application 'kwin_x11' crashing...