Do not call glDrawBuffersARB when the extension is absent

gpu/command_buffer/service/framebuffer_manager.cc

Index: gpu/command_buffer/service/framebuffer_manager.cc
diff --git a/gpu/command_buffer/service/framebuffer_manager.cc b/gpu/command_buffer/service/framebuffer_manager.cc
index 4022b3defaa1e286e85e72f7ac6aa702fa1e9fb2..e1426c7d9689a3db8120a5fd4c3caba73625fc8f 100644
--- a/gpu/command_buffer/service/framebuffer_manager.cc
+++ b/gpu/command_buffer/service/framebuffer_manager.cc
@@ -374,6 +374,11 @@ bool Framebuffer::HasUnclearedColorAttachments() const {
 }
 
 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;