NTP SI messages should only be shown the first time a NTP SI is shown

[LaurenWags]

Description

Found while testing #7883

The first time a SNTP is viewed, a dismiss-able message is shown in some cases. Currently this message is only dismissed manually via the X. However, per discussion with @petemill and in the spec, this introductory message should only be shown to the user the first time they are seeing a sponsored image.

From the spec:

The introductory message, which is shown only to users seeing a sponsored image for the first time. 

Steps to Reproduce

Multiple scenarios, but here are two
Scenario 1

1. Clean profile
2. Rewards ON, Ads ON, Widget ON
3. Enable flag for SNTP
4. Relaunch
5. Open NTP until SNTP is shown. Note message is displayed as expected and could be dismissed manually. Do not dismiss it. (edit[@petemill]: Make sure page stays active for at least 4 seconds)
6. Open or refresh until another SNTP is shown.

Scenario 2

1. Clean profile
2. Rewards OFF, Widget OFF
3. Enable flag for SNTP
4. Relaunch
5. Open NTP until SNTP is shown. Note message is displayed as expected and could be dismissed manually. Do not dismiss it. (edit[@petemill]: Make sure page stays active for at least 4 seconds)
6. Open or refresh until another SNTP is shown.

Actual result:

Message is shown on second SNTP.
Scenario 1:

Scenario 2:

Expected result:

Message should not be shown on the second SNTP

Reproduces how often:

easily

Brave version (brave://version info)

1.5.62

Version/Channel Information:

• Can you reproduce this issue with the current release? n/a
• Can you reproduce this issue with the beta channel? n/a
• Can you reproduce this issue with the dev channel? n/a
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

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

Miscellaneous Information:

cc @brave/legacy_qa @rebron @petemill

[GeetaSarvadnya]

Reproduced in windows 10 x64

Brave	1.5.63 Chromium: 79.0.3945.130 (Official Build) nightly (64-bit)
Revision	e22de67c28798d98833a7137c0e22876237fc40a-refs/branch-heads/3945@{#1047}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

Found 2 more scenarios which are listed below

Scenario 3:

1. Clean profile
2. Enable flag for SNTP
3. Enable rewards and disable ads
4. Open NTP until SNTP is shown (once the SNTP message is shown don't dismiss it)
5. Open NTP until SNTP is shown
   Actual: Message is shown on 2nd SNTP also
   

Scenario 4:

1. Clean profile
2. Enable flag for SNTP
3. Enable rewards and disable Brave Rewards switch
4. Open NTP until SNTP is shown (once the SNTP message is shown don't dismiss it)
5. Open NTP until SNTP is shown
   Actual: Message is shown on 2nd SNTP also
   

[rebron]

@petemill I moved to 1.3.x - Release milestone.