Shotdown browser cooperatively with taskill on win platform.

tools/telemetry/telemetry/core/platform/__init__.py

Index: tools/telemetry/telemetry/core/platform/__init__.py
diff --git a/tools/telemetry/telemetry/core/platform/__init__.py b/tools/telemetry/telemetry/core/platform/__init__.py
index 1f77028115aa46c6b82b776f908f1b417ed80333..3f95c39d5658d704a9d21196139f4db658cc5b37 100644
--- a/tools/telemetry/telemetry/core/platform/__init__.py
+++ b/tools/telemetry/telemetry/core/platform/__init__.py
@@ -326,3 +326,34 @@ class Platform(object):
       }
     """
     return self._platform_backend.StopMonitoringPower()
+
+  def IsProcessRunning(self, proc):
+    """ Return True if given process from subprocess.Popen is running. """
+    return self._platform_backend.IsProcessRunning(proc)
+
+  def StopProcess(self, proc):
+    """Cooperatively shut down the given process from subprocess.Popen.
+
+    Returns True if it is believed the attempt succeeded."""
+    assert self.IsProcessRunning(proc), 'Process is not running'
+    if self._platform_backend.IsCooperativeShutdownSupported():
+      self._platform_backend.CooperativelyShutdown(proc)
+      try:
+        util.WaitFor(lambda: not self.IsProcessRunning(proc), timeout=5)
+        return True
+      except util.TimeoutException:
+        return False
+    else:
+      return False
+
+  def KillProcess(self, proc):
+    """ Kill given process from subprocess.Popen forcefully.
+
+    Returns True if it is believed the attempt succeeded."""
+    assert self.IsProcessRunning(proc), 'Process is not running'
+    self._proc.kill()
+    try:
+      util.WaitFor(lambda: not self.IsProcessRunning(proc), timeout=5)
+      return True
+    except util.TimeoutException:
+      assert False