Make all the content corner images the same size.

Some of these were 38 px high and some 37.  They should have all been 38.  This
bit me when trying to change corner layout to measure a different one of the
images' height.  It might have also resulted in small gaps in drawing of the
content "border"; I didn't look closely.  I did check that things are correct
with the new images.

Since the bottom section of each image is just the same row of pixels over and
over, it's easy to expand the height.  Did this, then compressed the images with
optimize_png_files.sh -o2.

BUG=none
TEST=none
TBR=oshima

Review URL: https://codereview.chromium.org/1427433015 .

Cr-Commit-Position: refs/heads/master@{#358718}
3 files changed