Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message.

content/common/child_process_host_impl.h

Index: content/common/child_process_host_impl.h
diff --git a/content/common/child_process_host_impl.h b/content/common/child_process_host_impl.h
index 1576489acb97972402a98d40d9a47bd3b302f2bf..2cd9967a48d050074ad132f02eac718f2f977b92 100644
--- a/content/common/child_process_host_impl.h
+++ b/content/common/child_process_host_impl.h
@@ -40,6 +40,11 @@
                                             public IPC::Listener {
  public:
   ~ChildProcessHostImpl() override;
+
+  // Public and static for reuse by RenderMessageFilter.
+  static void AllocateSharedMemory(
+      size_t buffer_size, base::ProcessHandle child_process,
+      base::SharedMemoryHandle* handle);
 
   // Returns a unique ID to identify a child process. On construction, this
   // function will be used to generate the id_, but it is also used to generate
@@ -88,6 +93,8 @@
 
   // Message handlers:
   void OnShutdownRequest();
+  void OnAllocateSharedMemory(uint32_t buffer_size,
+                              base::SharedMemoryHandle* handle);
   void OnAllocateGpuMemoryBuffer(gfx::GpuMemoryBufferId id,
                                  uint32_t width,
                                  uint32_t height,