[Telemetry] Fix @Cache to maintain cache for life of instance for bound methods

tools/telemetry/telemetry/decorators.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
+# pylint: disable=W0212
 
 import functools
+import inspect
 import types
 
 
 def Cache(obj):
   """Decorator for caching read-only properties.
 
   Example usage (always returns the same Foo instance):
     @Cache
     def CreateFoo():
       return Foo()
 
   If CreateFoo() accepts parameters, a separate cached value is maintained
   for each unique parameter combination.
+
+  Cached methods maintain their cache for the lifetime of the /instance/, while
+  cached functions maintain their cache for the lifetime of the /module/.
   """
-  cache = obj.__cache = {}
-
   @functools.wraps(obj)
   def Cacher(*args, **kwargs):
-    key = str(args) + str(kwargs)
-    if key not in cache:
-      cache[key] = obj(*args, **kwargs)
-    return cache[key]
+    cacher = args[0] if inspect.getargspec(obj).args[:1] == ['self'] else obj
+    cacher.__cache = cacher.__cache if hasattr(cacher, '__cache') else {}
+    key = str(obj) + str(args) + str(kwargs)
+    if key not in cacher.__cache:
+      cacher.__cache[key] = obj(*args, **kwargs)
+    return cacher.__cache[key]
   return Cacher
 
 
 def Disabled(*args):
   """Decorator for disabling tests/benchmarks.
 
   May be used without args to unconditionally disable:
     @Disabled  # Unconditionally disabled.
 
   If args are given, the test will be disabled if ANY of the args match the
@@ skipping 42 matching lines @@
     wrapper._enabled_strings = enabled_strings
     return wrapper
   assert args and not callable(args[0]), '@Enabled requires argumentas'
   enabled_strings = list(args)
   for enabled_string in enabled_strings:
     # TODO(tonyg): Validate that these strings are recognized.
     assert isinstance(enabled_string, str), '@Enabled accepts a list of strs'
   return _Enabled
 
 
-# pylint: disable=W0212
 def IsEnabled(test, possible_browser):
   """Returns True iff |test| is enabled given the |possible_browser|.
 
   Use to respect the @Enabled / @Disabled decorators.
 
   Args:
     test: A function or class that may contain _disabled_strings and/or
           _enabled_strings attributes.
     possible_browser: A PossibleBrowser to check whether |test| may run against.
   """
@@ skipping 33 matching lines @@
       if enabled_string in platform_attributes:
         return True
     print (
         'Skipping %s because it is only enabled for %s. '
         'You are running %s.' % (name,
                                  ' or '.join(enabled_strings),
                                  ' '.join(platform_attributes)))
     return False
 
   return True