Skip creating zygote with --no-zygote flag

This CL fixed the side effect of
https://chromium-review.googlesource.com/c/chromium/src/+/509529
By above commit, browser creates zygote process even with --no-sandbox
--no-zygote flags. Zygote process should not be created with
--no-sandbox --no-zygote flags.

Bug: 895732
Change-Id: I2e2bebbab69b4ac5047cc33aa346942b83a67183
Reviewed-on: https://chromium-review.googlesource.com/c/1282687
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602590}

content/app/content_main_runner_impl.cc

@@ -281,10 +281,12 @@ void InitializeZygoteSandboxForBrowserProcess(
   // zygote are both disabled. It initializes the sandboxed process socket.
   SandboxHostLinux::GetInstance()->Init();
 
-  if (parsed_command_line.HasSwitch(switches::kNoZygote) &&
-      !parsed_command_line.HasSwitch(service_manager::switches::kNoSandbox)) {
-    LOG(ERROR) << "--no-sandbox should be used together with --no--zygote";
-    exit(EXIT_FAILURE);
+  if (parsed_command_line.HasSwitch(switches::kNoZygote)) {
+    if (!parsed_command_line.HasSwitch(service_manager::switches::kNoSandbox)) {
+      LOG(ERROR) << "--no-sandbox should be used together with --no--zygote";
+      exit(EXIT_FAILURE);
+    }
+    return;
   }
 
   // Tickle the zygote host so it forks now.

content/test/BUILD.gn

@@ -1106,7 +1106,10 @@ test("content_browsertests") {
 
   if (is_linux) {
     sources += [ "../zygote/zygote_browsertest.cc" ]
-    deps += [ "//ui/gfx:test_support" ]
+    deps += [
+      "//services/service_manager/zygote",
+      "//ui/gfx:test_support",
+    ]
   }
 
   if (is_android) {

content/zygote/zygote_browsertest.cc

@@ -14,6 +14,10 @@
 #include "content/shell/browser/shell.h"
 #include "services/service_manager/embedder/switches.h"
 #include "services/service_manager/sandbox/switches.h"
+#include "services/service_manager/zygote/common/zygote_buildflags.h"
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+#include "services/service_manager/zygote/host/zygote_host_impl_linux.h"
+#endif
 
 namespace content {
 
@@ -67,4 +71,13 @@ IN_PROC_BROWSER_TEST_F(LinuxZygoteDisabledBrowserTest,
 }
 #endif
 
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+IN_PROC_BROWSER_TEST_F(LinuxZygoteDisabledBrowserTest,
+                       NoZygoteWhenZygoteDisabled) {
+  NavigateToURL(shell(), GURL("data:text/html,start page"));
+
+  EXPECT_FALSE(service_manager::ZygoteHostImpl::GetInstance()->HasZygote());
+}
+#endif
+
 }  // namespace content

services/service_manager/zygote/host/zygote_host_impl_linux.h

@@ -46,6 +46,7 @@ class COMPONENT_EXPORT(SERVICE_MANAGER_ZYGOTE) ZygoteHostImpl
 
   void AdjustRendererOOMScore(base::ProcessHandle process_handle,
                               int score) override;
+  bool HasZygote() { return !zygote_pids_.empty(); }
 
  private:
   friend struct base::DefaultSingletonTraits<ZygoteHostImpl>;