gpu: Enable OOP-R by default on mac.

The only blocker for this is the input latency regression which we hope
to recover with skbug.com/9455. But the regression is in the order of
4 to 11% at the 99th percentile, which is not severe enough to hold back
the rollout.

Bug: 757605
Change-Id: I77618b2b1de99c9367e85fa10a445f387380b243
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929637
Auto-Submit: Khushal <khushalsagar@chromium.org>
Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718965}

gpu/config/gpu_finch_features.cc

@@ -55,7 +55,7 @@ const base::Feature kDefaultEnableGpuRasterization{
 
 // Enable out of process rasterization by default.  This can still be overridden
 // by --enable-oop-rasterization or --disable-oop-rasterization.
-#if defined(OS_ANDROID) || defined(OS_CHROMEOS)
+#if defined(OS_ANDROID) || defined(OS_CHROMEOS) || defined(OS_MACOSX)
 const base::Feature kDefaultEnableOopRasterization{
     "DefaultEnableOopRasterization", base::FEATURE_ENABLED_BY_DEFAULT};
 #else