[telemetry] Add a webdriver backend with support for IE.

tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py

Index: tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py
diff --git a/tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py b/tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py
index 1da104085e281c376ebc938fe9db3fb26de66321..b952144156e42ada41871d03c36bf52e3ca85653 100644
--- a/tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py
+++ b/tools/telemetry/telemetry/core/chrome/desktop_browser_finder.py
@@ -15,9 +15,7 @@ from telemetry.core import possible_browser
 from telemetry.core import profile_types
 from telemetry.core.chrome import cros_interface
 from telemetry.core.chrome import desktop_browser_backend
-from telemetry.core.platform import linux_platform_backend
-from telemetry.core.platform import mac_platform_backend
-from telemetry.core.platform import win_platform_backend
+from telemetry.core.platform import util as platform_util
 
 ALL_BROWSER_TYPES = ','.join([
     'exact',
@@ -51,16 +49,8 @@ class PossibleDesktopBrowser(possible_browser.PossibleBrowser):
         self._options, self._local_executable, self._flash_path,
         self._is_content_shell,
         delete_profile_dir_after_run=delete_profile_dir_after_run)
-    if sys.platform.startswith('linux'):
-      p = linux_platform_backend.LinuxPlatformBackend()
-    elif sys.platform == 'darwin':
-      p = mac_platform_backend.MacPlatformBackend()
-    elif sys.platform == 'win32':
-      p = win_platform_backend.WinPlatformBackend()
-    else:
-      raise NotImplementedError()
-
-    b = browser.Browser(backend, p)
+    b = browser.Browser(backend,
+                        platform_util.CreatePlatformBackendForCurrentOS())
     backend.SetBrowser(b)
     return (b, backend)