Use command line to signal whether a child process was passed V8 snapshot files via file descriptor

ash/shell/content_client/shell_content_browser_client.cc

Index: ash/shell/content_client/shell_content_browser_client.cc
diff --git a/ash/shell/content_client/shell_content_browser_client.cc b/ash/shell/content_client/shell_content_browser_client.cc
index 7f956ec18344a884106e821237383d2ae6953764..51b0107d5ad9f1b8a532e3793655f9a506b1f193 100644
--- a/ash/shell/content_client/shell_content_browser_client.cc
+++ b/ash/shell/content_client/shell_content_browser_client.cc
@@ -5,7 +5,9 @@
 #include "ash/shell/content_client/shell_content_browser_client.h"
 
 #include "ash/shell/content_client/shell_browser_main_parts.h"
+#include "base/command_line.h"
 #include "content/public/common/content_descriptors.h"
+#include "content/public/common/content_switches.h"
 #include "content/shell/browser/shell_browser_context.h"
 #include "gin/v8_initializer.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ -41,6 +43,21 @@ net::URLRequestContextGetter* ShellContentBrowserClient::CreateRequestContext(
                                              request_interceptors.Pass());
 }
 
+void ShellContentBrowserClient::AppendExtraCommandLineSwitches(
+    base::CommandLine* command_line,
+    int child_process_id) {
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
+#if defined(V8_USE_EXTERNAL_STARTUP_DATA)
+  std::string process_type =
+      command_line->GetSwitchValueASCII(switches::kProcessType);
+  if (process_type != switches::kZygoteProcess) {
+    command_line->AppendSwitch(::switches::kV8NativesPassedByFD);
+    command_line->AppendSwitch(::switches::kV8SnapshotPassedByFD);
+  }
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+#endif  // OS_POSIX && !OS_MACOSX
+}
+
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
 void ShellContentBrowserClient::GetAdditionalMappedFilesForChildProcess(
     const base::CommandLine& command_line,