fix memory_test crashes
fix memory_test crashes

Memory tests run with plugins disabled.  WebKit r39969 changed
Page::pluginData to return null in this case, so we need to check
for this null.

This still won't work until we rev our webkit to r39988 which fixes
another crash.

Review URL: http://codereview.chromium.org/18375

git-svn-id: http://src.chromium.org/svn/trunk/src@8320 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 3c02f6146360bb0dcc2e04a25c31f1ecab2db3c5
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser