[Fuchsia] Disable GPU in webrunner

Now ContextProvider will run Context process with --disable-gpu.
GPU process doesn't work correctly on Fuchsia yet.

Bug: 850743, 867052
Change-Id: Ifde22a36beb69f187be07b7fd075a0f8d807bcdf
Reviewed-on: https://chromium-review.googlesource.com/1147550
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577663}

webrunner/service/context_provider_impl.cc

@@ -17,6 +17,7 @@
 #include "base/fuchsia/fuchsia_logging.h"
 #include "base/logging.h"
 #include "base/process/launch.h"
+#include "content/public/common/content_switches.h"
 #include "webrunner/service/common.h"
 
 namespace webrunner {
@@ -25,6 +26,8 @@ namespace {
 // Relaunches the current executable as a Context process.
 base::Process LaunchContextProcess(const base::LaunchOptions& launch_options) {
   base::CommandLine launch_command = *base::CommandLine::ForCurrentProcess();
+  // TODO(crbug.com/867052): Remove this flag when GPU process works on Fuchsia.
+  launch_command.AppendSwitch(switches::kDisableGpu);
   return base::LaunchProcess(launch_command, launch_options);
 }