More Chromium config tweaks

Following discussion at 312c2db06f (commitcomment-22173921)

config/chromium.conf

@@ -2,15 +2,13 @@
 # /usr/bin/chromium-browser
 
 # Options to pass to chromium-browser
-CHROMIUM_FLAGS="\
---disable-smooth-scrolling \
+CHROMIUM_FLAGS="--disable-smooth-scrolling \
 --disable-low-res-tiling \
 --enable-low-end-device-mode \
 --num-raster-threads=$(grep -c processor /proc/cpuinfo) \
 --profiler-timing=0 \
 --disable-composited-antialiasing \
---disk-cache-dir=/tmp/cache \
---disk-cache-size=$(df -B1 /tmp --output=source,avail | awk '/^tmpfs/ {printf ("%0.0f",$2*0.9); }') \
+--disk-cache-dir=/tmp/${USER}-cache \
+--disk-cache-size=$(findmnt --target /tmp -n -o AVAIL -b | awk '{printf ("%0.0f",$1*0.3); }') \
 --no-sandbox \
---test-type \
-"
+--test-type"