Fix OOM in TextureUpload perf test

The test texture size is reduced from 2k x 2k to 1k x 1k to avoid OOM on
lower-memory devices.

Bug: 945415
Change-Id: I66611417114212427f0a2cfc677450f5e705a7ca
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1537331
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>

src/tests/perf_tests/TextureUploadPerf.cpp

@@ -27,7 +27,7 @@ struct TextureUploadParams final : public RenderTestParams
         iterationsPerStep = kIterationsPerStep;
         trackGpuTime      = true;
 
-        baseSize     = 2048;
+        baseSize     = 1024;
         subImageSize = 64;
 
         webgl = false;