Teach GPU command buffer whether a context is webgl.

gpu/command_buffer/service/gles2_cmd_decoder.h

Index: gpu/command_buffer/service/gles2_cmd_decoder.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.h b/gpu/command_buffer/service/gles2_cmd_decoder.h
index 3fc862379787ac05c2861106cf56fc256e252e6f..f716fb3516abbb36517da62c4d11533987d82f17 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -45,10 +45,12 @@ struct ContextState;
 
 struct DisallowedFeatures {
   DisallowedFeatures()
-      : gpu_memory_manager(false) {
+      : gpu_memory_manager(false),
+        npot_support(false) {

[piman, 2015/06/08 21:40:21]

So, if we add this to the FeatureInfo, that could bring trouble - the
FeatureInfo is shared between all contexts in the same group, but in theory
today one can have a webgl context sharing with a non-webgl context (actually it
used to be that way but we removed it a little while ago).

I think it's a reasonable restriction, but it means we need to validate, when we
create the context, that the context group is compatible, otherwise fail.
Otherwise a NPOT texture would be valid/complete in one context and invalid in
another context and that violates a bunch of assumptions in the TextureManager.

[Zhenyao Mo, 2015/06/08 22:23:22]

I remember we decided each WebGL is in it's own context.  In the future we might
want to share WebGL contexts for shared resources extension purpose.  It seems
that we should not share WebGL and WebGL 2 contexts.

I can add the checks in, but should it be a CHECK/DCHECK or an initialization
failure?

   }
 
   bool gpu_memory_manager;
+  bool npot_support;
 };
 
 typedef base::Callback<void(const std::string& key,