Reduce diff to upstream re2 a bit.

third_party/re2/patches/this-null.patch

-Index: re2/prefilter.cc
-===================================================================
---- a/re2/prefilter.cc
-+++ b/re2/prefilter.cc
-@@ -265,14 +265,6 @@
- 
- // Format a Info in string form.
- string Prefilter::Info::ToString() {
--  if (this == NULL) {
--    // Sometimes when iterating on children of a node,
--    // some children might have NULL Info. Adding
--    // the check here for NULL to take care of cases where
--    // the caller is not checking.
--    return "";
--  }
--
-   if (is_exact_) {
-     int n = 0;
-     string s;
-@@ -640,7 +632,7 @@
- 
-   if (Trace) {
-     VLOG(0) << "BuildInfo " << re->ToString()
--            << ": " << info->ToString();
-+            << ": " << (info ? info->ToString() : "");
-   }
- 
-   return info;
-@@ -665,9 +657,6 @@
- }
- 
- string Prefilter::DebugString() const {
--  if (this == NULL)
--    return "<nil>";
--
-   switch (op_) {
-     default:
-       LOG(DFATAL) << "Bad op in Prefilter::DebugString: " << op_;
-@@ -683,7 +672,8 @@
-       for (int i = 0; i < subs_->size(); i++) {
-         if (i > 0)
-           s += " ";
--        s += (*subs_)[i]->DebugString();
-+        Prefilter* sub = (*subs_)[i];
-+        s += sub ? sub->DebugString() : "<nil>";
-       }
-       return s;
-     }
-@@ -692,7 +682,8 @@
-       for (int i = 0; i < subs_->size(); i++) {
-         if (i > 0)
-           s += "|";
--        s += (*subs_)[i]->DebugString();
-+        Prefilter* sub = (*subs_)[i];
-+        s += sub ? sub->DebugString() : "<nil>";
-       }
-       s += ")";
-       return s;
-Index: re2/regexp.cc
-===================================================================
---- a/re2/regexp.cc
-+++ b/re2/regexp.cc
-@@ -873,8 +873,6 @@
- }
- 
- void CharClass::Delete() {
--  if (this == NULL)
--    return;
-   uint8 *data = reinterpret_cast<uint8*>(this);
-   delete[] data;
- }