Hook up TABLET_MODE switch to maximize_mode_controller

ash/wm/maximize_mode/maximize_mode_controller.cc

Index: ash/wm/maximize_mode/maximize_mode_controller.cc
diff --git a/ash/wm/maximize_mode/maximize_mode_controller.cc b/ash/wm/maximize_mode/maximize_mode_controller.cc
index 9d8b18dae29de82390b61d4e439eca666dfd59db..9bf624e2c99fea7a6053e3dcc38f38073dc807c9 100644
--- a/ash/wm/maximize_mode/maximize_mode_controller.cc
+++ b/ash/wm/maximize_mode/maximize_mode_controller.cc
@@ -103,6 +103,9 @@ MaximizeModeController::MaximizeModeController()
       lid_open_past_180_(false),
       touchview_usage_interval_start_time_(base::Time::Now()),
       tick_clock_(new base::DefaultTickClock()),
+#if defined(OS_CHROMEOS)
+      tablet_mode_switch_was_on_(false),
+#endif
       lid_is_closed_(false) {
   Shell* shell = Shell::GetInstance();
   shell->AddShellObserver(this);
@@ -224,6 +227,18 @@ void MaximizeModeController::LidEventReceived(bool open,
   LeaveMaximizeMode();
 }
 
+void MaximizeModeController::TabletModeEventReceived(
+    bool on,
+    const base::TimeTicks& time) {
+  if (on) {
+    chromeos::AccelerometerReader::GetInstance()->RemoveObserver(this);
+    EnterMaximizeMode();
+  } else {
+    tablet_mode_switch_was_on_ = true;
+    chromeos::AccelerometerReader::GetInstance()->AddObserver(this);

[Daniel Erat, 2016/06/06 15:24:55]

this approach seems problematic. if powerd sends multiple notifications (e.g.
because it crashes and restarts, or the switch is malfunctioning, or there's a
kernel bug, or there's a firmware bug, or etc.), won't you double-add or
double-remove the observer? i wouldn't be surprised if that causing a failed
assert and crashes chrome.

what's wrong with the approach that i suggested?

[jcliang, 2016/06/06 16:48:36]

I didn't realize that {Add|Remove}Observer() are not protected against double
{add|remove}. The remove/add observers are not necessary and are just some
enhancements suggested by Jonathan.

We can factor out the state changing logic in HandleHingeRotation() to another
UpdateState() function, but it doesn't really solve the issue here. The problem
we have here is that we're depending on lid_open_past_180_ = true to leave
maximize mode, and we need to check if we need to leave maximize mode after
tablet mode switch if off. Setting lid_open_past_180_ or
tablet_mode_switch_was_on_ both were for this reason.

Now I think to solve this issue we should remove lid_open_past_180_, and replace
it with IsMaximizeModeManagerEnabled().

+  }
+}
+
 void MaximizeModeController::SuspendImminent() {
   // The system is about to suspend, so record TouchView usage interval metrics
   // based on whether TouchView mode is currently active.
@@ -255,6 +270,8 @@ void MaximizeModeController::HandleHingeRotation(
                                      kHingeVerticalSmoothingStart) /
                                         (kHingeVerticalSmoothingMaximum -
                                          kHingeVerticalSmoothingStart)));
+  bool is_base_vertical =
+      std::abs(base_reading.x()) > kHingeVerticalSmoothingMaximum;
 
   base_smoothed_.Scale(smoothing_ratio);
   base_reading.Scale(1.0f - smoothing_ratio);
@@ -277,7 +294,7 @@ void MaximizeModeController::HandleHingeRotation(
   if (lid_angle < 0.0f)
     lid_angle += 360.0f;
 
-  bool is_angle_stable = lid_angle >= kMinStableAngle &&
+  bool is_angle_stable = !is_base_vertical && lid_angle >= kMinStableAngle &&
                          lid_angle <= kMaxStableAngle;
 
   // Clear the last_lid_open_time_ for a stable reading so that there is less
@@ -287,9 +304,10 @@ void MaximizeModeController::HandleHingeRotation(
     last_lid_open_time_ = base::TimeTicks();
 
   // Toggle maximize mode on or off when corresponding thresholds are passed.
-  if (lid_open_past_180_ && is_angle_stable &&
+  if ((lid_open_past_180_ || tablet_mode_switch_was_on_) && is_angle_stable &&
       lid_angle <= kExitMaximizeModeAngle) {
     lid_open_past_180_ = false;
+    tablet_mode_switch_was_on_ = false;
     LeaveMaximizeMode();
   } else if (!lid_open_past_180_ && !lid_is_closed_ &&
              lid_angle >= kEnterMaximizeModeAngle &&