[py] Raise error for unsupported method

The Selenium wire protocol does not define a "set window rect" method
[1]. Although similar behavior can be achieved by composing available
methods, doing so could lead to observable differences with WebDriver
(for instance, depending on the order the methods are invoked) and cause
issues when migrating.

Immediately raise an exception if the `set_window_rect` method is
invoked for a browser which uses the Selenium wire protocol. Extend the
method's documentation to include a recommendation on how to update
call sites in a forward-compatible way.

[1] https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol

py/selenium/webdriver/remote/webdriver.py

@@ -31,7 +31,8 @@
 from .file_detector import FileDetector, LocalFileDetector
 from selenium.common.exceptions import (InvalidArgumentException,
                                         WebDriverException,
-                                        NoSuchCookieException)
+                                        NoSuchCookieException,
+                                        UnknownMethodException)
 from selenium.webdriver.common.by import By
 from selenium.webdriver.common.html5.application_cache import ApplicationCache
 
@@ -1222,7 +1223,9 @@ def get_window_rect(self):
     def set_window_rect(self, x=None, y=None, width=None, height=None):
         """
         Sets the x, y coordinates of the window as well as height and width of
-        the current window.
+        the current window. This method is only supported for W3C compatible
+        browsers; other browsers should use `set_window_position` and
+        `set_window_size`.
 
         :Usage:
             ::
@@ -1231,6 +1234,9 @@ def set_window_rect(self, x=None, y=None, width=None, height=None):
                 driver.set_window_rect(width=100, height=200)
                 driver.set_window_rect(x=10, y=10, width=100, height=200)
         """
+        if not self.w3c:
+            raise UnknownMethodException("set_window_rect is only supported for W3C compatible browsers")
+
         if (x is None and y is None) and (height is None and width is None):
             raise InvalidArgumentException("x and y or height and width need values")