Improve GN public header file checking

tools/gn/c_include_iterator.h

Index: tools/gn/c_include_iterator.h
diff --git a/tools/gn/c_include_iterator.h b/tools/gn/c_include_iterator.h
index 2a25ef6f95fa9e13bda9a3df0a8bf13257ff2c37..41c124617ad7814635c16ad42a38e2ad0463efab 100644
--- a/tools/gn/c_include_iterator.h
+++ b/tools/gn/c_include_iterator.h
@@ -8,32 +8,43 @@
 #include "base/basictypes.h"
 #include "base/strings/string_piece.h"
 
+class InputFile;
+class LocationRange;
+
 // Iterates through #includes in C source and header files.
 //
 // This only returns includes we want to check, which is user includes with
 // double-quotes: #include "..."
 class CIncludeIterator {
  public:
-  // The buffer pointed to must outlive this class.
-  CIncludeIterator(const base::StringPiece& file);
+  // The InputFile pointed to must outlive this class.
+  CIncludeIterator(const InputFile* input);
   ~CIncludeIterator();
 
-  // Fills in the string with the contents of the next include and returns
-  // true, or returns false if there are no more includes.
-  bool GetNextIncludeString(base::StringPiece* out);
+  // Fills in the string with the contents of the next include, and the
+  // location with where it came from, and returns true, or returns false if
+  // there are no more includes.
+  bool GetNextIncludeString(base::StringPiece* out, LocationRange* location);
 
   // Maximum numbef of non-includes we'll tolerate before giving up. This does
   // not count comments or preprocessor.
   static const int kMaxNonIncludeLines;
 
  private:
-  // Returns false on EOF, otherwise fills in the given line.
-  bool GetNextLine(base::StringPiece* line);
+  // Returns false on EOF, otherwise fills in the given line and the one-based
+  // line number into *line_number;
+  bool GetNextLine(base::StringPiece* line, int* line_number);
+
+  const InputFile* input_file_;
 
+  // This just points into input_file_.contents() for convenience.
   base::StringPiece file_;
 
+  // 0-based offset into the file.
   size_t offset_;
 
+  int line_number_;  // One-based. Indicates the last line we read.
+
   // Number of lines we've processed since seeing the last include (or the
   // beginning of the file) with some exceptions.
   int lines_since_last_include_;