Stop adding preloaded RawResources to MemoryCache

This CL stops adding preloaded RawResources to MemoryCache. This is needed
to match preloaded resources with requests with UseStreamOnResponse specified.

From the following reasons, I believe the performance impact is negligible.

 - Preloading matching is now decoupled from MemoryCache in general.
 - Loading resources can be shareable only in the same frame.
 - There is no speculative RawResource preload.

Bug: 652228
Change-Id: Icc5f7fc893702233cc45bc130eb13e6fcae919df
Reviewed-on: https://chromium-review.googlesource.com/516926
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#475770}
2 files changed