Implement EXT_draw_buffers WebGL extention support in command buffer.

webkit/gpu/webgraphicscontext3d_in_process_impl.cc

Index: webkit/gpu/webgraphicscontext3d_in_process_impl.cc
===================================================================
--- webkit/gpu/webgraphicscontext3d_in_process_impl.cc	(revision 187725)
+++ webkit/gpu/webgraphicscontext3d_in_process_impl.cc	(working copy)
@@ -1731,6 +1731,11 @@
   return false;
 }
 
+void WebGraphicsContext3DInProcessImpl::drawBuffersEXT(
+    WGC3Dsizei n, const WGC3Denum* bufs) {
+  NOTIMPLEMENTED();
+}
+
 GrGLInterface* WebGraphicsContext3DInProcessImpl::onCreateGrGLInterface() {
   return gfx::CreateInProcessSkiaGLBinding();
 }