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Make sure to add a renderer-side safebrowsing throttle in order
to check renderer initiated url loads using the safebrowsing API.
This also ensures that resource requests for e.g. .js and .svg
files are also checked. This approach matches the behavior in
WebView and Chrome. Due to the addition of methods the original
safebrowsing initialization sequence is slightly changed (see
below for details). Additionally the ResourceContext destruction
has to happen on the IO thread (see below for details).

In particular in this patch:
- Add and implement ExposeInterfacesToRenderer method to make
  sure renderer can execute safebrowsing calls.
- Move safebrowsing_service initialization to the
  ExposeInterfacesToRenderer() method because it is executed
  before CreateURLLoaderThrottles.
- Implement UrlLoaderThrottleProvider in weblayer/renderer/
  which amongst other things adds the
  safe_browsing::RendererURLLoaderThrottle.
- Implement RenderThreadStarted() and
  CreateURLLoaderThrottleProvider() methods for
  ContentRendererClient.
- Update build and deps files accordingly.
- Also make sure to destroy ResourceContext on the IO thread
  (otherwise profile destruction sequence can result in a
  DCHECK, see crbug.com/1029317).

BUG=1015418,1028659,1029317

Change-Id: I67482a450d1974a8b14cb07f4fbedd14e4983e7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1937173
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720726}