Add default shortcut for tracing Skia's GPU memory usage

Bug: 319164766
Test: comparing traces with debug.hwui.skia_tracing_enabled on and off
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:1083707b02d70e0ae09d1e31cf50fc7cc294987e)
Merged-In: Ie24e3b4705380ef143699f229469226df7b4913a
Change-Id: Ie24e3b4705380ef143699f229469226df7b4913a