[Telemetry] Speed up page cycler by another ~20%.

This reduces cycle time of one moz iteration from just under 4m to just over 3m.

It assumes that pids won't be re-used, which isn't totally valid, but I think
the chances of rolling over the pid space within a single benchmark is a low
enough risk that we should do this.

BUG=372489

Review URL: https://codereview.chromium.org/281723008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270139 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/platform/android_platform_backend.py

@@ -157,12 +157,12 @@ class AndroidPlatformBackend(
         break
     return child_pids
 
+  @decorators.Cache
   def GetCommandLine(self, pid):
-    ps = self._GetPsOutput(['pid', 'name'])
-    for curr_pid, curr_name in ps:
-      if int(curr_pid) == pid:
-        return curr_name
-    raise exceptions.ProcessGoneException()
+    ps = self._GetPsOutput(['pid', 'name'], pid)
+    if not ps:
+      raise exceptions.ProcessGoneException()
+    return ps[0][1]
 
   def GetOSName(self):
     return 'android'