chromium: Add installation of libGLESv2.so

The following errors occur when you start Chromium prior to this commit:

[2534:2534:0625/202928.673160:ERROR:gl_implementation.cc(246)] Failed to
load .../libexec/chromium/swiftshader/libGLESv2.so:
../libexec/chromium/swiftshader/libGLESv2.so: cannot open shared object
file: No such file or directory
[2534:2534:0625/202928.674434:ERROR:gpu_child_thread.cc(174)] Exiting
GPU process due to errors during initialization

While in theory we do not strictly need libGLESv2.so, in practice this
means that the GPU process isn't starting up at all which in turn leads
to crawling rendering performance on some sites.

So let's install all shared libraries in swiftshader.

I've tested this with the chromium.stable NixOS VM test and also locally
on my machine and the errors as well as the performance issues are gone.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>