Implement SharedMemory::NewAnonymousReadOnly(contents).

base/memory/shared_memory_posix.cc

Index: base/memory/shared_memory_posix.cc
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index efb0caf5bc9a29d805700c3abdad18ad6671a199..ee87f8b7863b8d8262c3d8ed13e0f664c90ff2ee 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -101,6 +101,55 @@ size_t SharedMemory::GetHandleLimit() {
   return base::GetMaxFds();
 }
 
+// static
+scoped_ptr<SharedMemory> SharedMemory::NewAnonymousReadOnly(
+    StringPiece contents) {
+  // This function theoretically can block on the disk, but realistically
+  // the temporary files we create will just go into the buffer cache
+  // and be deleted before they ever make it out to disk.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
+  FilePath path;
+  file_util::ScopedFILE writable_fp(
+      file_util::CreateAndOpenTemporaryShmemFile(&path, /*executable=*/false));
+  if (!writable_fp) {
+    LOG(ERROR) << "Failed to create temp shmem file.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  int readonly_fd = HANDLE_EINTR(open(path.value().c_str(), O_RDONLY));
+  if (readonly_fd < 0) {
+    PLOG(ERROR) << "Failed to reopen temp shmem file readonly.";
+    return scoped_ptr<SharedMemory>();
+  }
+  file_util::ScopedFD readonly_fd_closer(&readonly_fd);
+
+  if (unlink(path.value().c_str()))
+    PLOG(WARNING) << "unlink";
+
+  if (fwrite(contents.data(), 1, contents.size(), writable_fp.get()) !=
+      contents.size()) {
+    LOG(ERROR) << "Failed to write " << contents.size()
+               << " bytes to memory block.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  if (fclose(writable_fp.release()) != 0) {
+    PLOG(ERROR) << "Failed to flush contents of memory block.";
+    return scoped_ptr<SharedMemory>();
+  }
+
+  // Protect against people accidentally reopening as read/write.  It's still
+  // possible to intentionally fchmod() the FD back and then open it from /dev,
+  // but the renderer can't open from a filesystem path.
+  if (0 != fchmod(readonly_fd, S_IRUSR))
+    PLOG(DFATAL) << "Failed to make FD " << readonly_fd << " read-only";
+
+  return make_scoped_ptr(new SharedMemory(
+      FileDescriptor(*readonly_fd_closer.release(), /*iauto_close=*/false),
+      /*read_only=*/true));
+}
+
 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
   return CreateAnonymous(size) && Map(size);
 }