Do not call glDrawBuffersARB when the extension is absent

gpu/command_buffer/service/framebuffer_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/framebuffer_manager.h"
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "gpu/command_buffer/common/gles2_cmd_utils.h"
 #include "gpu/command_buffer/service/renderbuffer_manager.h"
 #include "gpu/command_buffer/service/texture_manager.h"
@@ skipping 356 matching lines @@
         it->first < GL_COLOR_ATTACHMENT0 + manager_->max_draw_buffers_) {
       const Attachment* attachment = it->second.get();
       if (!attachment->cleared())
         return true;
     }
   }
   return false;
 }
 
 void Framebuffer::ChangeDrawBuffersHelper(bool recover) const {
+  // There will always be only one buffer, GL_COLOR_ATTACHMENT0, if
+  // GL_ARB_draw_buffers is not present, even if this FBO has no attachment.
+  if (!gfx::g_driver_gl.ext.b_GL_ARB_draw_buffers)
+    return;
+
   scoped_ptr<GLenum[]> buffers(new GLenum[manager_->max_draw_buffers_]);
   for (uint32 i = 0; i < manager_->max_draw_buffers_; ++i)
     buffers[i] = GL_NONE;
   for (AttachmentMap::const_iterator it = attachments_.begin();
        it != attachments_.end(); ++it) {
     if (it->first >= GL_COLOR_ATTACHMENT0 &&
         it->first < GL_COLOR_ATTACHMENT0 + manager_->max_draw_buffers_) {
       buffers[it->first - GL_COLOR_ATTACHMENT0] = it->first;
     }
   }
@@ skipping 348 matching lines @@
        ++it) {
     TextureDetachObserver* observer = *it;
     observer->OnTextureRefDetachedFromFramebuffer(texture);
   }
 }
 
 }  // namespace gles2
 }  // namespace gpu