Shotdown browser cooperatively with taskill on win platform.

tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py

Index: tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
index e4e0ff2bbbb15c44ea74196bf128bd57f4f93e09..f6e7210e412336eba288651a63dea6986f5349af 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
@@ -219,7 +219,7 @@ class DesktopBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
     return self._tmp_profile_dir
 
   def IsBrowserRunning(self):
-    return self._proc and self._proc.poll() == None
+    return self.browser.platform.IsProcessRunning(self._proc)
 
   def GetStandardOutput(self):
     if not self._tmp_output_file:
@@ -329,18 +329,14 @@ class DesktopBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
   def Close(self):
     super(DesktopBrowserBackend, self).Close()
 
-    # Shutdown politely if the profile may be used again.
-    if self._output_profile_path and self.IsBrowserRunning():
-      self._proc.terminate()
-      try:
-        util.WaitFor(lambda: not self.IsBrowserRunning(), timeout=5)
-        self._proc = None
-      except util.TimeoutException:
-        logging.warning('Failed to gracefully shutdown. Proceeding to kill.')
+    if self.IsBrowserRunning():
+      self.browser.platform.StopProcess(self._proc)
 
     # Shutdown aggressively if the above failed or if the profile is temporary.
     if self.IsBrowserRunning():
-      self._proc.kill()
+      self.browser.platform.KillProcess(self._proc)
+    assert not self.IsBrowserRunning(), (
+        'Failed to shutdown browser process with pid %s' % self._proc.pid)
     self._proc = None
 
     if self._crash_service: