Avoid a potential race condition on mDisplays

Update: The HWC1 path needed to be updated in light of a change to
SurfaceFlinger.h. The build now works for both paths.

Original Message:

The race could occur when transitioning in/out of VR flinger mode.
It is now avoided by ensuring that the primary |DisplayDevice| is always
created once |mStateLock| is released, and ensuring that all accesses
to the primary |DisplayDevice| are guarded by |mStateLock|.

Bug: 36194616
Bug: 37249613
Test: Compiled for both HWC1 and HWC2 surface flinger builds.
      Normal behavior is unchanged. Explicitly testing the race
      condition required instrumenting code with sleep statements.

Change-Id: I0b00e857a3b2fd01948a888db2f0715d2a8204c1
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp b/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
index 5b5f1cf..dcb2913 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
@@ -315,7 +315,7 @@
     queryDisplayProperties(disp);
     // Do not teardown or recreate the primary display
     if (disp != HWC_DISPLAY_PRIMARY) {
-        mEventHandler.onHotplugReceived(disp, bool(connected));
+        mEventHandler.onHotplugReceived(this, disp, bool(connected));
     }
 }