Revert "Avoid testing antialiased boundary in ScreenshotSyncIntegrationTest."

This reverts commit 841c0dde.

Reason for revert: Have to revert Chrome change

Original change's description:
> Avoid testing antialiased boundary in ScreenshotSyncIntegrationTest.
> 
> Skia currently has a driver workaround that performans antialiased
> rectangle edge equation evalution in the fragment shader rather than
> vertex shader on Adreno 3xx GPUs. This was done because the interpolation
> of values computed in the vertex shader lacks enough precision to pass
> these tests. However, doing so has a negative performance impact. Skia
> tests run with the workaround removed show that in practice the visual
> difference is insignificant. Moreover, cc::GLRenderer also incurs these
> same errors as it uses the same antialiasing approach without the
> workaround and has shipped on Adreno 3xx devices for years with no known
> complaints about antialiasing quality/accuracy. We're better off
> reclaiming the performance and accepting a small hit to antialiasing
> accuracy.
> 
> Bug: 847984
> Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
> Change-Id: If1e62e0780a752179a75ddd57ccc7b24128c68ac
> Reviewed-on: https://chromium-review.googlesource.com/1129041
> Reviewed-by: Kenneth Russell <kbr@chromium.org>
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Cr-Commit-Position: refs/heads/master@{#573695}

TBR=bsalomon@google.com,zmo@chromium.org,kbr@chromium.org

Change-Id: Ib787aba372282504f047c129a9f0b3750668d1b0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 847984
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/1132274Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Cr-Commit-Position: refs/heads/master@{#573888}

content/test/gpu/gpu_tests/screenshot_sync_integration_test.py

@@ -119,12 +119,9 @@ class ScreenshotSyncIntegrationTest(gpu_integration_test.GpuIntegrationTest):
         "window.draw({{ red }}, {{ green }}, {{ blue }});",
         red=canvasRGB.r, green=canvasRGB.g, blue=canvasRGB.b)
     screenshot = tab.Screenshot(10)
-    # Avoid checking along antialiased boundary due to limited Ardeno 3xx
-    # interpolation precision (crbug.com/847984).
-    inset = 1
-    start_x = inset
-    start_y = inset
-    outer_size = 256 - inset
+    start_x = 10
+    start_y = 0
+    outer_size = 256
     skip = 10
     for y in range(start_y, outer_size, skip):
       for x in range(start_x, outer_size, skip):