Added GPU driver workaround for OSX multimonitor multisampling disabling

content/browser/gpu/gpu_data_manager_impl_private.cc

Index: content/browser/gpu/gpu_data_manager_impl_private.cc
diff --git a/content/browser/gpu/gpu_data_manager_impl_private.cc b/content/browser/gpu/gpu_data_manager_impl_private.cc
index 98656dfdd68ccffbf7f02be7ae4f9f663d753a74..fc94c8f44851254aa3291905938fac0f48899dd8 100644
--- a/content/browser/gpu/gpu_data_manager_impl_private.cc
+++ b/content/browser/gpu/gpu_data_manager_impl_private.cc
@@ -229,7 +229,7 @@ std::string IntSetToString(const std::set<int>& list) {
 void DisplayReconfigCallback(CGDirectDisplayID display,
                              CGDisplayChangeSummaryFlags flags,
                              void* gpu_data_manager) {
-  if(flags == kCGDisplayBeginConfigurationFlag)
+  if (flags == kCGDisplayBeginConfigurationFlag)
     return; // This call contains no information about the display change
 
   GpuDataManagerImpl* manager =
@@ -376,6 +376,10 @@ bool GpuDataManagerImplPrivate::IsFeatureBlacklisted(int feature) const {
   return (blacklisted_features_.count(feature) == 1);
 }
 
+bool GpuDataManagerImplPrivate::IsDriverBugWorkaroundActive(int feature) const {
+  return (gpu_driver_bugs_.count(feature) == 1);
+}
+
 size_t GpuDataManagerImplPrivate::GetBlacklistedFeatureCount() const {
   if (use_swiftshader_)
     return 1;
@@ -817,8 +821,9 @@ void GpuDataManagerImplPrivate::UpdateRendererWebPrefs(
     prefs->flash_stage3d_baseline_enabled = false;
   if (IsFeatureBlacklisted(gpu::GPU_FEATURE_TYPE_ACCELERATED_2D_CANVAS))
     prefs->accelerated_2d_canvas_enabled = false;
-  if (IsFeatureBlacklisted(gpu::GPU_FEATURE_TYPE_MULTISAMPLING)
-      || display_count_ > 1)
+  if (IsFeatureBlacklisted(gpu::GPU_FEATURE_TYPE_MULTISAMPLING) ||
+      (IsDriverBugWorkaroundActive(gpu::DISABLE_MULTIMONITOR_MULTISAMPLING) &&
+          display_count_ > 1))
     prefs->gl_multisampling_enabled = false;
   if (IsFeatureBlacklisted(gpu::GPU_FEATURE_TYPE_3D_CSS)) {
     prefs->accelerated_compositing_for_3d_transforms_enabled = false;