add graphics_WebGLClear client test

The graphics_WebGLClear client test is a simple test to gauge
the glClear performance on any particular client.

v2: set preserve_srcdir=True; don't bother installing again if
    version hasn't changed.

v3: minor style fixes; improved/added comment sections; change
    width/height of context; fix copyrights; fix control file
    constants; added graphics state checker to test; add test
    to perf dashboard config.

BUG=chromium:397666
TEST=Manually created/updated ebuilds, then execute:
TEST= cros_workon-{B} start autotest-deps-webgl-clear autotest-chrome
TEST= emerge-{B} autotest-deps-webgl-clear
TEST= TESTS="graphics_WebGLClear" emerge-{B} autotest-chrome
TEST= ./run_remote_tests.sh --use_emerged --remote <ip> graphics_WebGLClear

Change-Id: I67d3358eee36a52f18a88c7bf944336d913b2a7d
Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/209675
Reviewed-by: Ilja Friedel <ihf@chromium.org>
Commit-Queue: Joe Konno <joe.konno@intel.com>
7 files changed