Unsafe memory write in BraveNetworkDelegateBase

[iefremov]

Description

In BraveNetworkDelegateBase::GetReferralHeaders()[1] pointer is written on UI thread, at the some moment it could be read on IO thread.

[1] https://github.com/brave/brave-core/blob/master/browser/net/brave_network_delegate_base.cc#L86

Brave version (brave://version info)

Brave	0.62.0 Chromium: 72.0.3626.71 (Developer Build) (64-bit)
Revision	f52ccad2a6a3c65fc9e0c591a517ceab1198dac0-refs/branch-heads/3626@{#763}

Reproducible on current release:

yes

[rebron]

cc: @brave/legacy_qa please see pr for details

[btlechowski]

Verification passed on

Brave	0.62.25 Chromium: 73.0.3683.67 (Official Build) beta (64-bit)
Revision	a83fd4f3207ae83412d329a9ca1239dd1e068345-refs/branch-heads/3683@{#760}
OS	Windows 7 Service Pack 1 Build 7601.24312

Test plan is based on this comment: brave/brave-core#1531 (comment)
Verified marketwatch.com and barrons.com got X-Brave-Partner: dowjones header
Verified cheddar.com got X-Brave-Partner: cheddar header
Verified coinbase.com got x-brave-partner: coinbase header

Verification PASSED on macOS 10.14.3 x64 using the following build:

Brave	0.62.27 Chromium: 73.0.3683.75 (Official Build) beta(64-bit)
Revision	909ee014fcea6828f9a610e6716145bc0b3ebf4a-refs/branch-heads/3683@{#803}
OS	Mac OS X

• Went through the test plan mentioned under Fix concurrency brave-core#1531 (comment) and ensured the following:
  • Verified marketwatch.com and barrons.com displayed the X-Brave-Partner: dowjones header
  • Verified cheddar.com received the X-Brave-Partner: cheddar header
  • Verified coinbase.com received the x-brave-partner: coinbase header