Make ddg search engine provider enable in guest window

[simonhong]

Description

DDG setting doesn't work in guest window

Steps to Reproduce

1. Open guest window
2. Turn on ddg in ntp
3. Check ddg is used

Actual result:

ddg isn't used

Expected result:

search engine provider should be ddg when ddg prefs is turned on

Reproduces how often:

Brave version (chrome://version info)

Reproducible on current release:

• Does it reproduce on brave-browser dev/beta builds?
• Does it reproduce on browser-laptop?

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
• Is the issue reproducible on the latest version of Chrome?

Additional Information

[btlechowski]

Verification passed on

Brave	0.55.12 Chromium: 70.0.3538.45 (Official Build) (64-bit)
Revision	cbdc32e4334458954e9def214d7e5fa1ca1960eb-refs/branch-heads/3538@{#830}
OS	Windows 7

Verification passed on

Brave	0.55.12 Chromium: 70.0.3538.45 (Official Build) (64-bit)
Revision	cbdc32e4334458954e9def214d7e5fa1ca1960eb-refs/branch-heads/3538@{#830}
OS	Windows 7

• Enabling DDG doesn't update the URL Bar message until mouse over. But DDG works fine

Verified passed with

Brave	0.55.12 Chromium: 70.0.3538.45 (Official Build) beta(64-bit)
Revision	cbdc32e4334458954e9def214d7e5fa1ca1960eb-refs/branch-heads/3538@{#830}
OS	Mac OS X