Ensure Linux minidump writer flushes minidump header early.

src/client/linux/minidump_writer/minidump_writer.cc

 // Copyright (c) 2010, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 150 matching lines @@
     if (fd_ == -1)
       minidump_writer_.Close();
     dumper_->ThreadsResume();
   }
 
   bool Dump() {
     // A minidump file contains a number of tagged streams. This is the number
     // of stream which we write.
     unsigned kNumWriters = 13;
 
-    TypedMDRVA<MDRawHeader> header(&minidump_writer_);
     TypedMDRVA<MDRawDirectory> dir(&minidump_writer_);
-    if (!header.Allocate())
-      return false;
-    if (!dir.AllocateArray(kNumWriters))
-      return false;
-    my_memset(header.get(), 0, sizeof(MDRawHeader));
+    {
+      // Ensure the header gets flushed, as that happens in the destructor.
+      // If a crash occurs somewhere below, at least the header will be
+      // intact.
+      TypedMDRVA<MDRawHeader> header(&minidump_writer_);
+      if (!header.Allocate())
+        return false;
 
-    header.get()->signature = MD_HEADER_SIGNATURE;
-    header.get()->version = MD_HEADER_VERSION;
-    header.get()->time_date_stamp = time(NULL);
-    header.get()->stream_count = kNumWriters;
-    header.get()->stream_directory_rva = dir.position();
+      if (!dir.AllocateArray(kNumWriters))
+        return false;
+
+      my_memset(header.get(), 0, sizeof(MDRawHeader));
+
+      header.get()->signature = MD_HEADER_SIGNATURE;
+      header.get()->version = MD_HEADER_VERSION;
+      header.get()->time_date_stamp = time(NULL);
+      header.get()->stream_count = kNumWriters;
+      header.get()->stream_directory_rva = dir.position();
+    }
 
     unsigned dir_index = 0;
     MDRawDirectory dirent;
 
     if (!WriteThreadListStream(&dirent))
       return false;
     dir.CopyIndex(dir_index++, &dirent);
 
     if (!WriteMappings(&dirent))
       return false;
@@ skipping 1157 matching lines @@
                    const MappingList& mappings,
                    const AppMemoryList& appmem,
                    LinuxDumper* dumper) {
   MinidumpWriter writer(filename, -1, NULL, mappings, appmem, dumper);
   if (!writer.Init())
     return false;
   return writer.Dump();
 }
 
 }  // namespace google_breakpad