GPU-CTS Program

Add new application, called GPU-CTS (GPU Compatibility Test Suite),
which executes skia gms against OpenGL and Vulkan backends.  Makes use
of googletest library for consistancy with Android CTS programs.

Add googletest to DEPS

gm_knowledge.h header as a stub for future work on validating gm output.

gm_runner can be re-used in other programs.  Talks to Skia and GM with a
simple API.

gpuctx executable wraps gm_runner and googletest together.

Change-Id: Ie7350b22164fa73e44121c39b0f36da4038a700b
Reviewed-on: https://skia-review.googlesource.com/56601
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/DEPS b/DEPS
index 7eb63b3..77453c1 100644
--- a/DEPS
+++ b/DEPS
@@ -7,6 +7,7 @@
   "third_party/externals/dng_sdk"       : "https://android.googlesource.com/platform/external/dng_sdk.git@96443b262250c390b0caefbf3eed8463ba35ecae",
   "third_party/externals/expat"         : "https://android.googlesource.com/platform/external/expat.git@android-6.0.1_r55",
   "third_party/externals/freetype"      : "https://skia.googlesource.com/third_party/freetype2.git@447a0b62634802d8acdb56008cff5ff4e50be244",
+  "third_party/externals/googletest"    : "https://android.googlesource.com/platform/external/googletest@dd43b9998e9a44a579a7aba6c1309407d1a5ed95",
   "third_party/externals/harfbuzz"      : "https://skia.googlesource.com/third_party/harfbuzz.git@1.4.2",
   "third_party/externals/icu"           : "https://chromium.googlesource.com/chromium/deps/icu.git@ec9c1133693148470ffe2e5e53576998e3650c1d",
   "third_party/externals/imgui"         : "https://github.com/ocornut/imgui.git@6384eee34f08cb7eab8d835043e1738e4adcdf75",