[WebGL 2] primitive restart should be always enabled

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 5a0bfcb6f9ff5b278fd104149c67f368b88ac648..8d49b6524aedbcd3c7fc92bed5e13d7c67d1c7e6 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6154,12 +6154,30 @@ void GLES2DecoderImpl::DoFramebufferRenderbuffer(
 }
 
 void GLES2DecoderImpl::DoDisable(GLenum cap) {
+  if (cap == GL_PRIMITIVE_RESTART_FIXED_INDEX) {
+    // TODO(Yunchao): crbug.com/594021
+    // On Desktop GL with versions lower than 4.3, we need to emulate
+    // GL_PRIMITIVE_RESTART_FIXED_INDEX using glPrimitiveRestartIndex().
+    if (feature_info_->feature_flags().emulate_primitive_restart_fixed_index) {
+      return;

[Ken Russell (switch to Gerrit), 2016/03/19 00:06:41]

This short-circuit here and in DoEnable looks wrong to me. The
SetCapabilityState call is always needed -- that's how the command buffer tracks
whether the state is enabled or disabled. For the emulation on OpenGL <4.3, the
only thing that should be skipped is the glDisable/glEnable call.

+    }
+    buffer_manager()->SetPrimitiveRestartState(false);
+  }
   if (SetCapabilityState(cap, false)) {
     glDisable(cap);
   }
 }
 
 void GLES2DecoderImpl::DoEnable(GLenum cap) {
+  if (cap == GL_PRIMITIVE_RESTART_FIXED_INDEX) {
+    // TODO(Yunchao): crbug.com/594021
+    // On Desktop GL with versions lower than 4.3, we need to emulate
+    // GL_PRIMITIVE_RESTART_FIXED_INDEX using glPrimitiveRestartIndex().
+    if (feature_info_->feature_flags().emulate_primitive_restart_fixed_index) {
+      return;
+    }
+    buffer_manager()->SetPrimitiveRestartState(true);
+  }
   if (SetCapabilityState(cap, true)) {
     glEnable(cap);
   }