Ensure Linux minidump writer flushes minidump header early.

src/client/linux/minidump_writer/minidump_writer.cc

Index: src/client/linux/minidump_writer/minidump_writer.cc
diff --git a/src/client/linux/minidump_writer/minidump_writer.cc b/src/client/linux/minidump_writer/minidump_writer.cc
index 9a0a830b13723b02cdec7930c4e49e4e5d4044d1..04327338b81d55cc84c97d2898bd1d0ad25f39b7 100644
--- a/src/client/linux/minidump_writer/minidump_writer.cc
+++ b/src/client/linux/minidump_writer/minidump_writer.cc
@@ -168,19 +168,26 @@ class MinidumpWriter {
     // 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;