Hook ANGLE_request_extension up to the passthrough cmd decoder.

third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 84 matching lines @@
     scoped.context()->m_framebufferBinding->drawBuffers(buffers);
   }
 }
 
 // static
 bool WebGLDrawBuffers::satisfiesWebGLRequirements(
     WebGLRenderingContextBase* webglContext) {
   gpu::gles2::GLES2Interface* gl = webglContext->contextGL();
   Extensions3DUtil* extensionsUtil = webglContext->extensionsUtil();
 
+  if (!extensionsUtil->isExtensionEnabled("GL_EXT_draw_buffers")) {
+    // Extension can be enabled but is not yet so we trust that the command
+    // decoder has full support
+    return true;

[Zhenyao Mo, 2017/02/06 22:31:38]

So when we actually try to enable this extension, this function may return
false. Will this cause problems?

[Geoff Lang, 2017/02/07 19:01:15]

The comment below says that we can only get here if GL_EXT_draw_buffers is
supported but it's not very clear that it can be supported but not enabled yet. 
I added a new method to Extensions3DUtil, isExtensionRequestable, to make it
more readable.

+  }
+
   // This is called after we make sure GL_EXT_draw_buffers is supported.
   GLint maxDrawBuffers = 0;
   GLint maxColorAttachments = 0;
   gl->GetIntegerv(GL_MAX_DRAW_BUFFERS_EXT, &maxDrawBuffers);
   gl->GetIntegerv(GL_MAX_COLOR_ATTACHMENTS_EXT, &maxColorAttachments);
   if (maxDrawBuffers < 4 || maxColorAttachments < 4)
     return false;
 
   GLuint fbo;
   gl->GenFramebuffers(1, &fbo);
@@ skipping 72 matching lines @@
   if (supportsDepth)
     gl->DeleteTextures(1, &depth);
   if (supportsDepthStencil)
     gl->DeleteTextures(1, &depthStencil);
   gl->DeleteTextures(colors.size(), colors.data());
 
   return ok;
 }
 
 }  // namespace blink