Add python coverage 3.7 to depot tools.

third_party/coverage/backward.py

Index: third_party/coverage/backward.py
diff --git a/third_party/coverage/backward.py b/third_party/coverage/backward.py
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+"""Add things to old Pythons so I can pretend they are newer."""
+
+# This file does lots of tricky stuff, so disable a bunch of lintisms.
+# pylint: disable=F0401,W0611,W0622
+# F0401: Unable to import blah
+# W0611: Unused import blah
+# W0622: Redefining built-in blah
+
+import os, re, sys
+
+# Python 2.3 doesn't have `set`
+try:
+    set = set       # new in 2.4
+except NameError:
+    from sets import Set as set
+
+# Python 2.3 doesn't have `sorted`.
+try:
+    sorted = sorted
+except NameError:
+    def sorted(iterable):
+        """A 2.3-compatible implementation of `sorted`."""
+        lst = list(iterable)
+        lst.sort()
+        return lst
+
+# Python 2.3 doesn't have `reversed`.
+try:
+    reversed = reversed
+except NameError:
+    def reversed(iterable):
+        """A 2.3-compatible implementation of `reversed`."""
+        lst = list(iterable)
+        return lst[::-1]
+
+# rpartition is new in 2.5
+try:
+    "".rpartition
+except AttributeError:
+    def rpartition(s, sep):
+        """Implement s.rpartition(sep) for old Pythons."""
+        i = s.rfind(sep)
+        if i == -1:
+            return ('', '', s)
+        else:
+            return (s[:i], sep, s[i+len(sep):])
+else:
+    def rpartition(s, sep):
+        """A common interface for new Pythons."""
+        return s.rpartition(sep)
+
+# Pythons 2 and 3 differ on where to get StringIO
+try:
+    from cStringIO import StringIO
+    BytesIO = StringIO
+except ImportError:
+    from io import StringIO, BytesIO
+
+# What's a string called?
+try:
+    string_class = basestring
+except NameError:
+    string_class = str
+
+# Where do pickles come from?
+try:
+    import cPickle as pickle
+except ImportError:
+    import pickle
+
+# range or xrange?
+try:
+    range = xrange
+except NameError:
+    range = range
+
+# A function to iterate listlessly over a dict's items.
+try:
+    {}.iteritems
+except AttributeError:
+    def iitems(d):
+        """Produce the items from dict `d`."""
+        return d.items()
+else:
+    def iitems(d):
+        """Produce the items from dict `d`."""
+        return d.iteritems()
+
+# Exec is a statement in Py2, a function in Py3
+if sys.version_info >= (3, 0):
+    def exec_code_object(code, global_map):
+        """A wrapper around exec()."""
+        exec(code, global_map)
+else:
+    # OK, this is pretty gross.  In Py2, exec was a statement, but that will
+    # be a syntax error if we try to put it in a Py3 file, even if it is never
+    # executed.  So hide it inside an evaluated string literal instead.
+    eval(
+        compile(
+            "def exec_code_object(code, global_map):\n"
+            "    exec code in global_map\n",
+            "<exec_function>", "exec"
+            )
+        )
+
+# Reading Python source and interpreting the coding comment is a big deal.
+if sys.version_info >= (3, 0):
+    # Python 3.2 provides `tokenize.open`, the best way to open source files.
+    import tokenize
+    try:
+        open_source = tokenize.open     # pylint: disable=E1101
+    except AttributeError:
+        from io import TextIOWrapper
+        detect_encoding = tokenize.detect_encoding  # pylint: disable=E1101
+        # Copied from the 3.2 stdlib:
+        def open_source(fname):
+            """Open a file in read only mode using the encoding detected by
+            detect_encoding().
+            """
+            buffer = open(fname, 'rb')
+            encoding, _ = detect_encoding(buffer.readline)
+            buffer.seek(0)
+            text = TextIOWrapper(buffer, encoding, line_buffering=True)
+            text.mode = 'r'
+            return text
+else:
+    def open_source(fname):
+        """Open a source file the best way."""
+        return open(fname, "rU")
+
+
+# Python 3.x is picky about bytes and strings, so provide methods to
+# get them right, and make them no-ops in 2.x
+if sys.version_info >= (3, 0):
+    def to_bytes(s):
+        """Convert string `s` to bytes."""
+        return s.encode('utf8')
+
+    def to_string(b):
+        """Convert bytes `b` to a string."""
+        return b.decode('utf8')
+
+    def binary_bytes(byte_values):
+        """Produce a byte string with the ints from `byte_values`."""
+        return bytes(byte_values)
+
+    def byte_to_int(byte_value):
+        """Turn an element of a bytes object into an int."""
+        return byte_value
+
+    def bytes_to_ints(bytes_value):
+        """Turn a bytes object into a sequence of ints."""
+        # In Py3, iterating bytes gives ints.
+        return bytes_value
+
+else:
+    def to_bytes(s):
+        """Convert string `s` to bytes (no-op in 2.x)."""
+        return s
+
+    def to_string(b):
+        """Convert bytes `b` to a string (no-op in 2.x)."""
+        return b
+
+    def binary_bytes(byte_values):
+        """Produce a byte string with the ints from `byte_values`."""
+        return "".join([chr(b) for b in byte_values])
+
+    def byte_to_int(byte_value):
+        """Turn an element of a bytes object into an int."""
+        return ord(byte_value)
+
+    def bytes_to_ints(bytes_value):
+        """Turn a bytes object into a sequence of ints."""
+        for byte in bytes_value:
+            yield ord(byte)
+
+# Md5 is available in different places.
+try:
+    import hashlib
+    md5 = hashlib.md5
+except ImportError:
+    import md5
+    md5 = md5.new