Data reduction proxy reconfigured on pref view

On Android, viewing the data reduction settings screen would
trigger configuring the proxy, even if the user did not change
the data reduction proxy enabled pref. This CL limits
reconfigurations to actual pref changes, which reduces the work
Chrome needs to do.

BUG=181049

Review URL: https://codereview.chromium.org/124793003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245138 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245138