Use static_cast instead of reinterpret_cast for downcasting

static_cast is better suited for downcasting since it can check that the
types are related.

/components/cronet
This CL was uploaded by git cl split.

R=ericorth@chromium.org

Change-Id: I4d485c7b43cdc9a755112f093e691f6077b13bdb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435753
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Eric Orth <ericorth@chromium.org>
Commit-Queue: Eric Orth <ericorth@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811301}

components/cronet/stale_host_resolver_unittest.cc

@@ -705,7 +705,7 @@ TEST_F(StaleHostResolverTest, CreatedByContext) {
   std::unique_ptr<net::URLRequestContext> context(builder.Build());
 
   // Experimental options ensure context's resolver is a StaleHostResolver.
-  SetResolver(reinterpret_cast<StaleHostResolver*>(context->host_resolver()),
+  SetResolver(static_cast<StaleHostResolver*>(context->host_resolver()),
               context.get());
   // Note: Experimental config above sets 0ms stale delay.
   CreateCacheEntry(kAgeExpiredSec, net::OK);