newtab background images use way too much RAM

[bridiver]

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  The newtab background images seem to use a lot of RAM and opening too many of them can cause the renderer to OOM crash because they all run in the same process

• Platform (Win7, 8, 10? macOS? Linux distro?):
  MacOS and maybe others

• Brave Version (revision SHA):
  57e6965

• Steps to reproduce:

  1. Open a newtab page
  2. Check memory usage
  3. Open more newtab pages

• Actual result:
  memory usage will increase very quickly and usually crash at around 10-20 newtab pages (depending on window/screen size)

• Expected result:
  memory usage should minimally increase and should not crash

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  0.13.0

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:

• Any related issues:

[bridiver]

several problems/solutions were discussed

1. The images are loaded both as a background image and an unused img tag
2. newtab pages can share a single webview (requires tear-off tab support to use across all windows)
3. may be missing some gpu acceleration