[blink] Only create metadata handler for document RawResources.

- RawResource is used for several non-text resources, as well as
  document resources. The cached metadata handling has been set up
  for a document's inline scripts. This makes it difficult to cache
  metadata properly for other RawResources, such as WebAssembly
  modules. This change only creates SourceKeyedMetadataHandler for
  RawResources whose type is kMainResource.
- Renames RawResource::CacheHandler to InlineScriptCacheHandler so
  it doesn't hide the Resource::CacheHandler method, and so we can
  later add other kinds of metadata handlers.

Bug: chromium:719172
Change-Id: I53f361a0df48dc9d73780971e3408dfff08de518
Reviewed-on: https://chromium-review.googlesource.com/1173496
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583684}
3 files changed