Replace ScriptSourceCode::GetResource() with CacheHandler()

As a result of preceding refactoring CLs,
ScriptSourceCode::GetResource() is no longer used, except for
getting its cache handler.
This CL removes GetResource() and instead introduces
ScriptSourceCode::CacheHandler(), to make it clearer that
ScriptSourceCode has all necessary information for compilation,
evaluation and code caching, without relying on ScriptResource.

Where CachedMetadataHandler was given separately,
this CL sets the CachedMetadataHandler to ScriptSourceCode
and removes the separate CachedMetadataHandler arguments.

Bug: 788828, 686281
Change-Id: I19555cafa7637bbb2289e9085baadd400e9987dd
Reviewed-on: https://chromium-review.googlesource.com/791493
Commit-Queue: Hiroshige Hayashizaki <[email protected]>
Reviewed-by: Kouhei Ueno <[email protected]>
Reviewed-by: Jeremy Roman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#522841}
12 files changed