Catch TabCrashException that may occur as we poll for oobe disappearing.

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

Index: tools/telemetry/telemetry/core/backends/chrome/misc_web_contents_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/misc_web_contents_backend.py b/tools/telemetry/telemetry/core/backends/chrome/misc_web_contents_backend.py
index f2327c0e6106aaeb9721839d95b627c16dd62bcc..891366b2643e766324285d4465124964967e7117 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/misc_web_contents_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/misc_web_contents_backend.py
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 import json
 
+from telemetry.core import exceptions
 from telemetry.core import web_contents
 from telemetry.core.backends.chrome import inspector_backend
 
@@ -17,7 +18,10 @@ class MiscWebContentsBackend(object):
     if oobe_web_contents_info:
       debugger_url = oobe_web_contents_info.get('webSocketDebuggerUrl')
       if debugger_url:
-        inspector = self._CreateInspectorBackend(debugger_url)
+        try:
+          inspector = self._CreateInspectorBackend(debugger_url)
+        except exceptions.TabCrashException:
+          return None
         return web_contents.WebContents(inspector)
     return None