Add GL_EXT_multisampled_render_to_texture support to command buffer.

gpu/command_buffer/service/context_group.cc

Index: gpu/command_buffer/service/context_group.cc
diff --git a/gpu/command_buffer/service/context_group.cc b/gpu/command_buffer/service/context_group.cc
index bbacc71490fa5023891d021612d00524c5f2a180..90932fbdddc43cf68e849c8c37d3fa1ce00e347d 100644
--- a/gpu/command_buffer/service/context_group.cc
+++ b/gpu/command_buffer/service/context_group.cc
@@ -101,8 +101,14 @@ bool ContextGroup::Initialize(
     return false;
   }
   GLint max_samples = 0;
-  if (feature_info_->feature_flags().chromium_framebuffer_multisample) {
-    glGetIntegerv(GL_MAX_SAMPLES, &max_samples);
+  if (feature_info_->feature_flags().chromium_framebuffer_multisample ||
+      feature_info_->feature_flags().multisampled_render_to_texture) {
+    if (feature_info_->feature_flags(
+            ).use_img_for_multisampled_render_to_texture) {
+      glGetIntegerv(GL_MAX_SAMPLES_IMG, &max_samples);
+    } else {
+      glGetIntegerv(GL_MAX_SAMPLES, &max_samples);
+    }
   }
 
   if (feature_info_->feature_flags().ext_draw_buffers) {