Android: Skip device list update no Android Kit is active

This adds workaround to reduce the load added by the update of the
Android device list, which currently happens in a polling style. Skip
an update if (*):
- The current open project is configured with a non-Android kit
- No project is open
- the current project target is null

To summarize the timeline of the timer used here:
- AndroidDeviceManager::setupDevicesWatcher() is called when Creator
is started or when settings are changed. The setup makes the connections
for the timeout and for AVD list future watcher. This will be done once.
If the timer is active it won't be done again, so no duplicate
connections.
- In the setup, the list of devices in updated once.
- On timer timeout, we attempt to update the list, however with
conditions listed in (*) as well as only when an Android adb path is
found.

Fixes: QTCREATORBUG-26547
Change-Id: I13312c4b507ce4e4064adb1c1342f4648f915394
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/plugins/android/androiddevice.cpp

@@ -37,7 +37,10 @@
 
 #include <projectexplorer/devicesupport/devicemanager.h>
 #include <projectexplorer/devicesupport/idevicewidget.h>
+#include <projectexplorer/kitinformation.h>
 #include <projectexplorer/runconfiguration.h>
+#include <projectexplorer/session.h>
+#include <projectexplorer/target.h>
 
 #include <utils/qtcprocess.h>
 #include <utils/runextensions.h>
@@ -418,11 +421,19 @@ QUrl AndroidDevice::toolControlChannel(const ControlChannelHint &) const
 
 void AndroidDeviceManager::updateDevicesList()
 {
-    connect(&m_devicesUpdaterTimer, &QTimer::timeout, this, [this]() {
+    // If a non-Android Kit is currently active, skip the device list update
+    const Target *startupTarget = SessionManager::startupTarget();
+    if (!startupTarget)
+        return;
+
+    const Kit *kit = startupTarget->kit();
+    if (!kit)
+        return;
+
+    if (DeviceTypeKitAspect::deviceTypeId(kit) != Constants::ANDROID_DEVICE_TYPE)
+        return;
+
     updateDevicesListOnce();
-    });
-    updateDevicesListOnce();
-    m_devicesUpdaterTimer.start(deviceUpdaterMsInterval);
 }
 
 void AndroidDeviceManager::updateDevicesListOnce()
@@ -537,11 +548,17 @@ void AndroidDeviceManager::setEmulatorArguments(QWidget *parent)
 
 void AndroidDeviceManager::setupDevicesWatcher()
 {
+    if (!m_devicesUpdaterTimer.isActive()) {
         // The call to avdmanager is always slower than the call to adb devices,
         // so connecting the slot to the slower call should be enough.
         connect(&m_avdsFutureWatcher, &QFutureWatcherBase::finished,
                 this,  &AndroidDeviceManager::devicesListUpdated);
+        connect(&m_devicesUpdaterTimer, &QTimer::timeout, this, [this]() {
             updateDevicesList();
+        });
+        m_devicesUpdaterTimer.start(deviceUpdaterMsInterval);
+    }
+    updateDevicesListOnce();
 }
 
 void AndroidDeviceManager::devicesListUpdated()