releasetools: Keep the original RangeSet for 'uses_shared_blocks' case.

Setting 'uses_shared_blocks' indicates that the block list for a given
file is incomplete, as some of the blocks are "owned" by others. As a
result, such a file will be skipped from imgdiff'ing.

This CL makes a copy of the original block list before removing the
shared blocks. It uses the original RangeSet as the value of
extra['uses_shared_blocks']. validate_target_files.py will try to read
the file as in the original RangeSet, unless the original list is also
incomplete or has non-monotonic ranges.

Test: Run validate_target_files on a target that uses
      `BOARD_EXT4_SHARE_DUP_BLOCKS := true`.
Change-Id: I259e871ecc249ba0c14b5796bef413185a1b8242

tools/releasetools/sparse_img.py

@@ -248,15 +248,21 @@ class SparseImage(object):
         ranges = rangelib.RangeSet.parse(ranges)
 
         if allow_shared_blocks:
-          # Find the shared blocks that have been claimed by others.
+          # Find the shared blocks that have been claimed by others. If so, tag
+          # the entry so that we can skip applying imgdiff on this file.
           shared_blocks = ranges.subtract(remaining)
           if shared_blocks:
-            ranges = ranges.subtract(shared_blocks)
-            if not ranges:
+            non_shared = ranges.subtract(shared_blocks)
+            if not non_shared:
               continue
 
-            # Tag the entry so that we can skip applying imgdiff on this file.
-            ranges.extra['uses_shared_blocks'] = True
+            # There shouldn't anything in the extra dict yet.
+            assert not ranges.extra, "Non-empty RangeSet.extra"
+
+            # Put the non-shared RangeSet as the value in the block map, which
+            # has a copy of the original RangeSet.
+            non_shared.extra['uses_shared_blocks'] = ranges
+            ranges = non_shared
 
         out[fn] = ranges
         assert ranges.size() == ranges.intersect(remaining).size()