[CR elements] inherit font family for cr-link-row

This CL fixes the font family when overriding a <button> element with
is="cr-link-row". <button> was defaulting to Arial. This CL will inherit
its parents font family, which for MD WebUI is Roboto (with some fallbacks).

Bug: 795362
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I3303425f2dd2e10c95a7f30bf6b919ec7140d4be
Reviewed-on: https://chromium-review.googlesource.com/830651Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524560}

ui/webui/resources/cr_elements/cr_link_row/cr_link_row.html

@@ -18,6 +18,7 @@
         cursor: pointer;
         display: flex;
         flex: 1;
+        font-family: inherit;
         font-size: 100%;  /* Specifically for Mac OSX, harmless elsewhere. */
         line-height: 154%;  /* 20px. */
         margin: 0;