Don't use --process-per-tab when running layout tests.

content/shell/app/shell_main_delegate.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/shell/app/shell_main_delegate.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/cpu.h"
 #include "base/files/file.h"
@@ skipping 148 matching lines @@
   if (command_line.HasSwitch(switches::kRunLayoutTest)) {
     EnableBrowserLayoutTestMode();
 
 #if BUILDFLAG(ENABLE_PLUGINS)
     if (!ppapi::RegisterBlinkTestPlugin(&command_line)) {
       *exit_code = 1;
       return true;
     }
 #endif
     command_line.AppendSwitch(cc::switches::kEnableGpuBenchmarking);
-    command_line.AppendSwitch(switches::kProcessPerTab);
     command_line.AppendSwitch(switches::kEnableLogging);
     command_line.AppendSwitch(switches::kAllowFileAccessFromFiles);
     // only default to a software GL if the flag isn't already specified.
     if (!command_line.HasSwitch(switches::kUseGpuInTests) &&
         !command_line.HasSwitch(switches::kUseGL)) {
       command_line.AppendSwitchASCII(
           switches::kUseGL,
           gl::GetGLImplementationName(gl::GetSoftwareGLImplementation()));
     }
     command_line.AppendSwitch(switches::kSkipGpuDataLoading);
@@ skipping 206 matching lines @@
 
   return renderer_client_.get();
 }
 
 ContentUtilityClient* ShellMainDelegate::CreateContentUtilityClient() {
   utility_client_.reset(new ShellContentUtilityClient);
   return utility_client_.get();
 }
 
 }  // namespace content