surfaceflinger: work around dumpsys lockup

Bug: 35806047
Test: manual
Change-Id: I047ddf0ef9eacd4df7da3c9d91118c3f1592a9eb
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 0713709..20cca39 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -231,6 +231,9 @@
 
     // thread-safe
     mutable Mutex mVsyncLock;
+
+    // XXX temporary workaround for b/35806047
+    mutable std::atomic<bool> mDumpMayLockUp;
 };
 
 class HWComposerBufferCache {