Allow idle/suspend with 3+ monitors attached

ui/display/chromeos/display_configurator.cc

 // Copyright 2014 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 "ui/display/chromeos/display_configurator.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 278 matching lines @@
       size = mode_info->size();
 
       for (size_t i = 0; i < states.size(); ++i) {
         const DisplayState* state = &states[i];
         (*requests)[i].mode = display_power[i] ? state->mirror_mode : NULL;
       }
       break;
     }
     case MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED:
     case MULTIPLE_DISPLAY_STATE_MULTI_EXTENDED: {
-      if ((new_display_state == MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED &&
-           states.size() != 2 && num_on_displays != 2) ||
-          (new_display_state == MULTIPLE_DISPLAY_STATE_MULTI_EXTENDED &&
-           num_on_displays <= 2)) {
+      if (new_display_state == MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED &&
+          states.size() != 2 && num_on_displays != 2) {
         LOG(WARNING) << "Ignoring request to enter extended mode with "
                      << states.size() << " connected display(s) and "
                      << num_on_displays << " turned on";
         return false;
       }

[oshima, 2016/07/15 23:58:15]

can you add comment that in docked mode, we may get multi_extended with 2
displays?

[dnicoara, 2016/07/18 14:19:02]

Actually the state would be MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED in that case.
We do a similar optimization for docked mode with one external display (and in
that case the state is MULTIPLE_DISPLAY_STATE_SINGLE). (See
UpdateDisplayConfigurationTask::ChooseDisplayState() for the details.)

I double checked that docked mode with 2 external displays works as expected.

I've added a comment to explain this. I'll wait for your ack before committing
just in case you think we should do more checks.

 
       for (size_t i = 0; i < states.size(); ++i) {
         const DisplayState* state = &states[i];
         (*requests)[i].origin.set_y(size.height() ? size.height() + kVerticalGap
                                                   : 0);
         (*requests)[i].mode = display_power[i] ? state->selected_mode : NULL;
 
         // Retain the full screen size even if all displays are off so the
         // same desktop configuration can be restored when the displays are
         // turned back on.
@@ skipping 841 matching lines @@
   last_virtual_display_id_ = max_display_id & 0xff;
 
   return true;
 }
 
 bool DisplayConfigurator::IsDisplayOn() const {
   return current_power_state_ != chromeos::DISPLAY_POWER_ALL_OFF;
 }
 
 }  // namespace ui