[top-chrome-md] Allows UpdateMaterialDesignColors to be called before MDC::Initialize()

BUG=622234

Review-Url: https://codereview.chromium.org/2089263002
Cr-Commit-Position: refs/heads/master@{#401707}
(cherry picked from commit 69730710ade45f4cb7502f7b0ffff1b09c6a4ec5)

Review URL: https://codereview.chromium.org/2171873002 .

Cr-Commit-Position: refs/branch-heads/2743@{#684}
Cr-Branched-From: 2b3ae3b8090361f8af5a611712fc1a5ab2de53cb-refs/heads/master@{#394939}
2 files changed