In the current version of the MSVC toolchain, it seems that the
compiler finds a near-match for the FlushInstructionCache call in
v8::internal::, so instead of looking in other namespaces for matching
overrides it emits this error:

C2660: 'v8::internal::FlushInstructionCache': function does not take 3 arguments

This change works around this by explicitly stating the expected
namespace.

Bug: chromium:927113
Change-Id: Ie39d6fdd458646fc86a4a2b16a93d6888ef1a5ae
Reviewed-on: https://chromium-review.googlesource.com/c/1462260Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59644}