Move content::MakeSharedMemorySegmentViaIPC into its own file

content/common/child_process_sandbox_support_impl_linux.h

Index: content/common/child_process_sandbox_support_impl_linux.h
diff --git a/content/common/child_process_sandbox_support_impl_linux.h b/content/common/child_process_sandbox_support_impl_linux.h
index 29b103ba75b8ac49cd4e923caf044ec9aaabf1d5..fb1558214a92475a05ff449d61b2b4f3c005d561 100644
--- a/content/common/child_process_sandbox_support_impl_linux.h
+++ b/content/common/child_process_sandbox_support_impl_linux.h
@@ -6,6 +6,8 @@
 #define CONTENT_COMMON_CHILD_PROCESS_SANDBOX_SUPPORT_IMPL_LINUX_H_
 #pragma once
 
+#include "base/global_descriptors_posix.h"
+#include "content/common/chrome_descriptors.h"
 #include "content/public/common/child_process_sandbox_support_linux.h"
 
 namespace WebKit {
@@ -31,6 +33,10 @@ void GetFontFamilyForCharacters(const uint16_t* utf16,
 void GetRenderStyleForStrike(const char* family, int sizeAndStyle,
                              WebKit::WebFontRenderStyle* out);
 
+inline int GetSandboxFD() {
+  return kSandboxIPCChannel + base::GlobalDescriptors::kBaseDescriptor;
+}
+
 };  // namespace content
 
 #endif  // CONTENT_COMMON_CHILD_PROCESS_SANDBOX_SUPPORT_IMPL_LINUX_H_