Make telemetry platform a singleton

tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py

Index: tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py
diff --git a/tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py b/tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py
index ae0a39ed5685c742724a6993d6667b49ba5e6d35..a9f6ac965ed277be224fd3d6dcc15cabafcf4c65 100644
--- a/tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py
+++ b/tools/telemetry/telemetry/core/backends/webdriver/webdriver_desktop_browser_finder.py
@@ -11,7 +11,7 @@ from telemetry.core import browser
 from telemetry.core import possible_browser
 from telemetry.core import util
 from telemetry.core.backends.webdriver import webdriver_ie_backend
-from telemetry.core.platform import factory
+from telemetry.core import platform as platform_module
 from telemetry.util import support_binaries
 
 # Try to import the selenium python lib which may be not available.
@@ -43,16 +43,18 @@ class PossibleWebDriverBrowser(possible_browser.PossibleBrowser):
     assert browser_type in ALL_BROWSER_TYPES, \
         'Please add %s to ALL_BROWSER_TYPES' % browser_type
 
-  @property
-  def _platform_backend(self):
-    return factory.GetPlatformBackendForCurrentOS()
+  def _InitPlatformIfNeeded(self):
+    if self._platform:
+      return
+    self._platform = platform_module.GetHostPlatform()
 
-  def CreateWebDriverBackend(self, platform_backend):
+  def _CreateWebDriverBrowserBackend(self):
     raise NotImplementedError()
 
   def Create(self):
-    backend = self.CreateWebDriverBackend(self._platform_backend)
-    return browser.Browser(backend, self._platform_backend)
+    self._InitPlatformIfNeeded()
+    backend = self._CreateWebDriverBrowserBackend()
+    return browser.Browser(backend, self._platform)
 
   def SupportsOptions(self, finder_options):
     if len(finder_options.extensions_to_load) != 0:
@@ -72,14 +74,14 @@ class PossibleDesktopIE(PossibleWebDriverBrowser):
     super(PossibleDesktopIE, self).__init__(browser_type, finder_options)
     self._architecture = architecture
 
-  def CreateWebDriverBackend(self, platform_backend):
+  def _CreateWebDriverBrowserBackend(self):
     assert webdriver
     def DriverCreator():
       ie_driver_exe = support_binaries.FindPath(
           'IEDriverServer_%s' % self._architecture, 'win')
       return webdriver.Ie(executable_path=ie_driver_exe)
     return webdriver_ie_backend.WebDriverIEBackend(
-        platform_backend, DriverCreator, self.finder_options.browser_options)
+        DriverCreator, self.finder_options.browser_options)
 
 def SelectDefaultBrowser(_):
   return None