Add MachOImageReader and its test

util/mac/mach_o_image_segment_reader.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
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   //!     MachOImageReader::GetSectionAtIndex(), this is a 0-based index. This
   //!     parameter must be in the range of valid indices aas reported by
   //!     nsects().
   //!
   //! \return A pointer to the section information. If \a index is out of range,
   //!     execution is aborted.
   //!
   //! \note The process_types::section::addr field gives the section’s preferred
   //!     load address as stored in the Mach-O image file, and is not adjusted
   //!     for any “slide” that may have occurred when the image was loaded.
+  //! \note Unlike MachOImageReader::GetSectionAtIndex(), this method does not
+  //!     accept out-of-range values for \a index, and aborts execution instead
+  //!     of returning `NULL` upon encountering an out-of-range value. This is
+  //!     because this method is expected to be used in a loop that can be
+  //!     limited to nsects() iterations, so an out-of-range error can be
+  //!     treated more harshly as a logic error, as opposed to a data error.
   //!
   //! \sa MachOImageReader::GetSectionAtIndex()
   const process_types::section* GetSectionAtIndex(size_t index) const;
 
+  //! Returns whether the segment slides.
+  //!
+  //! Most segments slide, but the __PAGEZERO segment does not, it grows
+  //! instead. This method identifies non-sliding segments in the same way that
+  //! the kernel does.
+  bool SegmentSlides() const;
+
   //! \brief Returns a segment name string.
   //!
   //! Segment names may be 16 characters long, and are not necessarily
   //! `NUL`-terminated. This function will return a segment name based on up to
   //! the first 16 characters found at \a segment_name_c.
   static std::string SegmentNameString(const char* segment_name_c);
 
   //! \brief Returns a section name string.
   //!
   //! Section names may be 16 characters long, and are not necessarily
@@ skipping 30 matching lines @@
   std::map<std::string, size_t> section_map_;
 
   InitializationStateDcheck initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(MachOImageSegmentReader);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_MAC_MACH_O_IMAGE_SEGMENT_READER_H_