Add GL_EXT_color_buffer_half_float support

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 3bb365ad1496b55ef0beca28e552d325443874be..98274c7d055719f56e078ff036e85810f3175b59 100644
--- a/gpu/command_buffer/service/context_group.cc
+++ b/gpu/command_buffer/service/context_group.cc
@@ -52,6 +52,9 @@ DisallowedFeatures AdjustDisallowedFeatures(
     adjusted_disallowed_features.ext_color_buffer_float = true;
     adjusted_disallowed_features.oes_texture_float_linear = true;
   }
+  if (context_type == CONTEXT_TYPE_WEBGL2) {
+    adjusted_disallowed_features.ext_color_buffer_half_float = true;

[Zhenyao Mo, 2017/02/23 05:49:10]

This also needs to be disallowed for WebGL1 because the extension has to be
explicitly enabled later.

+  }
   return adjusted_disallowed_features;
 }