Enable context virtualization only for GL

Only the GL back-end requires context virtualization. So only
require it for that case and not for Vulkan back-end.

Test: dEQP with ANGLE and ANGLE build with args.gn with
angle_enable_gl=false
Bug: 150892231

Change-Id: I443841c2543d0c6446d0f11122bf18dc9acbf428
diff --git a/opengl/libs/EGL/egl_display.cpp b/opengl/libs/EGL/egl_display.cpp
index 67d69b4..a58e87c 100644
--- a/opengl/libs/EGL/egl_display.cpp
+++ b/opengl/libs/EGL/egl_display.cpp
@@ -158,13 +158,16 @@
             // NOTE: This is only valid if the backend is OpenGL
             attrs.push_back(EGL_PLATFORM_ANGLE_EGL_HANDLE_ANGLE);
             attrs.push_back(vendorEGL);
+
+            // Context virtualization is only available on GL back-end.
+            // Needed to support threading with GL back-end
+            attrs.push_back(EGL_PLATFORM_ANGLE_CONTEXT_VIRTUALIZATION_ANGLE);
+            attrs.push_back(EGL_FALSE);
             break;
         default:
-            ALOGV("%s: Requesting Unknown (%d) ANGLE back-end", __FUNCTION__, cnx->angleBackend);
+            ALOGE("%s: Requesting Unknown (%d) ANGLE back-end", __FUNCTION__, cnx->angleBackend);
             break;
     }
-    attrs.push_back(EGL_PLATFORM_ANGLE_CONTEXT_VIRTUALIZATION_ANGLE);
-    attrs.push_back(EGL_FALSE);
 
     return true;
 }