Resize extension action icons to 16x16 in material design

Shrink the 19x19 extension action icons to 16x16
in top chrome material design so they match the
size and alignment of the other icons in the toolbar.

BUG=546206
TEST=manual

Review URL: https://codereview.chromium.org/1454753002

Cr-Commit-Position: refs/heads/master@{#360103}
1 file changed