Display currently running tests as the keepalive message.

Display currently running tests as the keepalive message.

...
( 466MB   550) 31.9ms   gpu gm colorwheelnative
( 466MB   549) 50.1ms   gpu gm colorwheel
( 468MB   548) 512ms    gpu gm colortype_xfermodes
Currently running:
    unit test PathOpsRectsThreaded
    unit test PathOpsSimplifyDegeneratesThreaded
    unit test PathOpsSimplifyQuadralateralsThreaded
    gpu gm colortype

( 468MB   547) 90.8ms   gpu gm colortype
( 469MB   546) 2.03s    unit test PathOpsSimplifyDegeneratesThreaded
...

BUG=skia:

Review URL: https://codereview.chromium.org/1017903002