Add transport security state generator tests.

net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc

Index: net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc
diff --git a/net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc b/net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc
index 5add4ead22c9fb2ba3fe3512674c17dcc494e519..e9e8f4b9a684e0d9599930e2db2dc4650d3cd7b4 100644
--- a/net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc
+++ b/net/tools/transport_security_state_generator/trie/trie_bit_buffer.cc
@@ -71,16 +71,19 @@ uint8_t TrieBitBuffer::BitLength(uint32_t input) const {
   return number_of_bits;
 }
 
-void TrieBitBuffer::WriteChar(uint8_t byte,
+bool TrieBitBuffer::WriteChar(uint8_t byte,
                               const HuffmanRepresentationTable& table,
                               HuffmanBuilder* huffman_builder) {
   HuffmanRepresentationTable::const_iterator item;
   item = table.find(byte);
-  DCHECK(item != table.end());
+  if (item == table.end()) {
+    return false;
+  }
   if (huffman_builder) {
     huffman_builder->RecordUsage(byte);
   }
   WriteBits(item->second.bits, item->second.number_of_bits);
+  return true;
 }
 
 void TrieBitBuffer::AppendBitsElement(uint8_t bits, uint8_t number_of_bits) {