Do not enter Maximize Mode while docked

ash/common/wm/maximize_mode/maximize_mode_controller.cc

Index: ash/common/wm/maximize_mode/maximize_mode_controller.cc
diff --git a/ash/common/wm/maximize_mode/maximize_mode_controller.cc b/ash/common/wm/maximize_mode/maximize_mode_controller.cc
index ef07902244ecc33649b4b503a17bb766184afe73..13c7b1f2a4c70f2574c4ebc0e9aaa45ac4705702 100644
--- a/ash/common/wm/maximize_mode/maximize_mode_controller.cc
+++ b/ash/common/wm/maximize_mode/maximize_mode_controller.cc
@@ -226,6 +226,9 @@ void MaximizeModeController::TabletModeEventReceived(
     bool on,
     const base::TimeTicks& time) {
   tablet_mode_switch_is_on_ = on;
+  // Do not change if docked.
+  if (!display::Display::HasInternalDisplay())
+    return;
   if (on && !IsMaximizeModeWindowManagerEnabled())
     EnterMaximizeMode();
 }
@@ -359,6 +362,10 @@ void MaximizeModeController::OnDisplayConfigurationChanged() {
       !WmShell::Get()->IsActiveDisplayId(
           display::Display::InternalDisplayId())) {
     LeaveMaximizeMode();
+  } else if (tablet_mode_switch_is_on_) {

[gwendal, 2017/01/23 20:48:31]

not enough: what if the use is in tent mode, and the tablet_mode_switch_is_on_
has not kicked in yet?

Ok, that's a corner case, but we should check the lid angle as well if
measurable.

[jonross, 2017/01/23 21:08:30]

With the internal display back on we will automatically go back to checking
accelerometer values. This has been how we have been handling exiting docked
mode historically.

The difference is only when tablet_mode_switch_is_on_ as we exit accelerometer
checks while that is true. So right now we wouldn't enter tablet mode.

I can update the docs here to be more explicit, and add a test for both.

+    // The internal display has returned, as we are exiting docked mode.
+    // The device is still in tablet mode, so trigger maximize mode.
+    EnterMaximizeMode();
   }
 }