Add a //nogncheck anntation to GN include checker

tools/gn/c_include_iterator.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/c_include_iterator.h"
 
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/location.h"
@@ skipping 87 matching lines @@
   size_t terminator_index = contents.find(terminating_char, 1);
   if (terminator_index == base::StringPiece::npos)
     return INCLUDE_NONE;
 
   *path = contents.substr(1, terminator_index - 1);
   // Note: one based so we do "+ 1".
   *begin_char = static_cast<int>(path->data() - line.data()) + 1;
   return type;
 }
 
+// Returns true if this line has a "nogncheck" comment associated with it.
+bool HasNoCheckAnnotation(const base::StringPiece& line) {
+  return line.find("nogncheck") != base::StringPiece::npos;
+}
+
 }  // namespace
 
 const int CIncludeIterator::kMaxNonIncludeLines = 10;
 
 CIncludeIterator::CIncludeIterator(const InputFile* input)
     : input_file_(input),
       file_(input->contents()),
       offset_(0),
       line_number_(0),
       lines_since_last_include_(0) {
 }
 
 CIncludeIterator::~CIncludeIterator() {
 }
 
 bool CIncludeIterator::GetNextIncludeString(base::StringPiece* out,
                                             LocationRange* location) {
   base::StringPiece line;
   int cur_line_number = 0;
   while (lines_since_last_include_ <= kMaxNonIncludeLines &&
          GetNextLine(&line, &cur_line_number)) {
     base::StringPiece include_contents;
     int begin_char;
     IncludeType type = ExtractInclude(line, &include_contents, &begin_char);
-    if (type == INCLUDE_USER) {
+    if (type == INCLUDE_USER && !HasNoCheckAnnotation(line)) {
       // Only count user includes for now.
       *out = include_contents;
       *location = LocationRange(
           Location(input_file_,
                    cur_line_number,
                    begin_char,
                    -1 /* TODO(scottmg): Is this important? */),
           Location(input_file_,
                    cur_line_number,
                    begin_char + static_cast<int>(include_contents.size()),
@@ skipping 19 matching lines @@
   line_number_++;
 
   *line = file_.substr(begin, offset_ - begin);
   *line_number = line_number_;
 
   // If we didn't hit EOF, skip past the newline for the next one.
   if (offset_ < file_.size())
     offset_++;
   return true;
 }