rangelib.py: Add parse_raw() method.

parse_raw() parses a string generated by RangeSet.to_string_raw().

>>> RangeSet.parse_raw(RangeSet("0-9").to_string_raw())
<RangeSet("0-9")>

Change-Id: Ia74daa30476d5e9ad73c368f4ecc64c755b734a5
diff --git a/tools/releasetools/rangelib.py b/tools/releasetools/rangelib.py
index 975a48a..31ed83a 100644
--- a/tools/releasetools/rangelib.py
+++ b/tools/releasetools/rangelib.py
@@ -71,6 +71,19 @@
     """
     return cls(text)
 
+  @classmethod
+  def parse_raw(cls, text):
+    """Parse a string generated by RangeSet.to_string_raw().
+
+    >>> RangeSet.parse_raw(RangeSet("0-9").to_string_raw())
+    <RangeSet("0-9")>
+    """
+
+    raw = [int(i) for i in text.split(',')]
+    assert raw[0] == len(raw[1:]), "Invalid raw string."
+
+    return cls(data=raw[1:])
+
   def _parse_internal(self, text):
     data = []
     last = -1