Revert of Wait 60s instead of 30s for browser to launch. (patchset #1 id:1 of...

Revert of Wait 60s instead of 30s for browser to launch. (patchset #1 id:1 of https://codereview.chromium.org/691683002/)

Reason for revert:
Didn't help -- stuck subprocesses are still showing up.

Original issue's description:
> Wait 60s instead of 30s for browser to launch.
>
> There's a guess that the browser may be launching extremely slowly on
> some bots and that when the browser main process is killed it's
> leaking sub-processes that are in the middle of being spawned.
> Increase the timeout to try to confirm this hypothesis.
>
> BUG=424024
> R=tonyg@chromium.org
>
> Committed: https://crrev.com/7ef2c0036f70bdcc59dd7c8f23c8b7c5a3f114d9
> Cr-Commit-Position: refs/heads/master@{#302087}

TBR=tonyg@chromium.org,nednguyen@google.com
NOTREECHECKS=true
NOTRY=true
BUG=424024

Review URL: https://codereview.chromium.org/667733004

Cr-Commit-Position: refs/heads/master@{#302128}

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

@@ -176,7 +176,7 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
 
   def _WaitForBrowserToComeUp(self, wait_for_extensions=True):
     try:
-      util.WaitFor(self.HasBrowserFinishedLaunching, timeout=60)
+      util.WaitFor(self.HasBrowserFinishedLaunching, timeout=30)
     except (util.TimeoutException, exceptions.ProcessGoneException) as e:
       if not self.IsBrowserRunning():
         raise exceptions.BrowserGoneException(self.browser, e)