Currently webrunner fails to start, crashing when trying to start GPU process. There are 3 separate bugs:

1. GPU process is being started even though the browser process is started with --disable-gpu . This started happening after https://chromium-review.googlesource.com/1170040 which enabled swiftsharer on Fuchsia (because swiftshader is enabled in headless ozone platform now). When swiftshader is enabled browser process starts GPU process even with --disable-gpu. It doesn't verify if SwiftShader is supported by the current Ozone platform (see https://codesearch.chromium.org/chromium/src/content/browser/gpu/gpu_data_manager_impl_private.cc?sq=package:chromium&dr&g=0&l=321 ). On Fuchsia SwiftShader is supported by headless ozone, but not in Scenic. 

2. GPU process crashes when the list of GL impls is empty, see InitializeGLOneOffHelper(), while Scenic ozone platform currently returns empty list of allowed GL implementations. We should either fix InitializeGLOneOffHelper() to handle this case or update Ozone platform to allow SwiftShader.

[02890.104] [1280646:1375011783:0815/181153.530695:FATAL:gl_factory.cc(34)] Check failed: !allowed_impls.empty().
[02890.104] bt#00: pc 0x3bb76894737f (app:/pkg/bin/app,0x86e337f)
[02890.104] bt#01: pc 0x3bb768722b8c (app:/pkg/bin/app,0x84beb8c)
[02890.104] bt#02: pc 0x3bb7687201fa (app:/pkg/bin/app,0x84bc1fa)
[02890.104] bt#03: pc 0x3bb76a5325ff (app:/pkg/bin/app,0xa2ce5ff) gl::init::(anonymous namespace)::InitializeGLOneOffHelper(bool) at //ui/gl/init/gl_factory.cc:?
[02890.104] bt#04: pc 0x3bb76a5337f8 (app:/pkg/bin/app,0xa2cf7f8) gl::init::InitializeGLNoExtensionsOneOff() at //ui/gl/init/gl_factory.cc:84


3. Browser doesn't handle GPU process crash properly, and also crashes:

[02890.117] [1280355:413355079:0815/181153.543820:FATAL:scoped_refptr.h(219)] Check failed: ptr_.
[02890.117] bt#00: pc 0x7cfb2fbd37f (app:/pkg/bin/app,0x86e337f)
[02890.117] bt#01: pc 0x7cfb2d98b8c (app:/pkg/bin/app,0x84beb8c)
[02890.117] bt#02: pc 0x7cfb2d961fa (app:/pkg/bin/app,0x84bc1fa)
[02890.117] bt#03: pc 0x7cfad3c17f2 (app:/pkg/bin/app,0x2ae77f2) scoped_refptr<network::ResourceRequestBody>::operator->() const at //base/memory/scoped_refptr.h:220
[02890.117] bt#04: pc 0x7cfae3cec19 (app:/pkg/bin/app,0x3af4c19) ~SandboxPolicyFuchsia at //content/common/sandbox_policy_fuchsia.cc:31
[02890.117] bt#05: pc 0x7cfafe5b631 (app:/pkg/bin/app,0x5581631) ~ChildProcessLauncherHelper at //content/browser/child_process_launcher_helper.cc:83
[02890.117] bt#06: pc 0x7cfafe5a967 (app:/pkg/bin/app,0x5580967) void base::RefCountedThreadSafe<content::internal::ChildProcessLauncherHelper, base::DefaultRefCountedThreadSafeTraits<content::internal::ChildProcessLauncherHelper> >::DeleteInternal<content::internal::ChildProcessLauncherHelper>(content::internal::ChildProcessLauncherHelper const*) at //base/memory/ref_counted.h:411

This issue is expected to be fixed in https://chromium-review.googlesource.com/c/chromium/src/+/1164539