PSA: Updating to windows SDK 10.0.26100.4654

[Devon Loehr]

We will soon be updating the packaged windows toolchain we use to build chromium to from SDK version 10.0.26100.3323 to 10.0.26100.4654. Googlers need take no action: they will automatically pull the new package when they run `gclient sync`. Those outside of Google should update their installed SDK using their normal methods.

For those wishing to reproduce our toolchain package, instructions are available in the CL. Note that we are no longer using an older version of d3dcompiler_47.dll, since its linking was fixed upstream.

Since this is a minor version bump, not much should change. However, please wait a week or so before making changes that depend on the new SDK version, to give time for it to settle and for developers to update their SDK installations.

--Devon Loehr