Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 9197d0cb264e99f6ea28f71a90f9fada6df650d8..04c1d09ace0bf7ee439130d489f77407434d3339 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -199,6 +199,11 @@
 #include "content/browser/mach_broker_mac.h"
 #endif
 
+#if defined(OS_POSIX)
+#include "content/browser/zygote_host/zygote_communication_linux.h"
+#include "content/browser/zygote_host/zygote_host_impl_linux.h"
+#endif  // defined(OS_POSIX)
+
 #if defined(USE_OZONE)
 #include "ui/ozone/public/client_native_pixmap_factory.h"
 #include "ui/ozone/public/ozone_platform.h"
@@ -387,12 +392,24 @@ class RendererSandboxedProcessLauncherDelegate
   }
 
 #elif defined(OS_POSIX)
-  bool ShouldUseZygote() override {
+  ZygoteHandle* GetZygote() override {
     const base::CommandLine& browser_command_line =
         *base::CommandLine::ForCurrentProcess();
     base::CommandLine::StringType renderer_prefix =
         browser_command_line.GetSwitchValueNative(switches::kRendererCmdPrefix);
-    return renderer_prefix.empty();
+    if (renderer_prefix.empty()) {
+      static ZygoteHandle zygote;
+#if !defined(OS_MACOSX) && !defined(OS_ANDROID)

[mdempsky, 2015/12/22 21:21:33]

We don't need the GetZygote function on OS X or Android anyway, so you could
also just completely #ifdef-out GetZygote on those platforms.  That would
actually be desirable too if it's not much trouble, because the linker can't do
dead code elimination on unused virtual functions (to my knowledge).

(Note: We do still need GetEnvironment and TakeIpcFd on OS X, but not on
Android.)

[Greg K, 2016/01/05 21:42:13]

Done.

+      if (zygote == nullptr) {
+        zygote = new ZygoteCommunication();
+        zygote->Init();
+        ZygoteHostImpl::GetInstance()->SetRendererSandboxStatus(

[mdempsky, 2015/12/22 21:21:33]

This is kind of clunky, though I don't have a better concrete suggestion off
hand.

I'm wondering if we could make the ZygoteHandle visible externally as a static
RenderProcessHostImpl::zygote_ or something, and then other code could directly
use RenderProcessHostImpl::zygote_->GetSandboxStatus(), but that might have race
conditions.  Hrm.

I'd suggest at least adding a TODO(kerrnel) or TODO(mdempsky) to investigate
later.

[Greg K, 2016/01/05 21:42:13]

Done.

+            zygote->GetSandboxStatus());
+      }
+#endif  // !OS_MACOSX && !defined(OS_ANDROID)
+      return &zygote;
+    }
+    return nullptr;
   }
   base::ScopedFD TakeIpcFd() override { return std::move(ipc_fd_); }
 #endif  // OS_WIN