Restart the engine within the docker container when appropriate.

blimp/engine/start_engine.sh

Index: blimp/engine/start_engine.sh
diff --git a/blimp/engine/start_engine.sh b/blimp/engine/start_engine.sh
index 519f31707744dfa56e4f4f65fa8da8586b5aac75..96c90d06913d2062ff7efcf090e67362ce8bde2a 100755
--- a/blimp/engine/start_engine.sh
+++ b/blimp/engine/start_engine.sh
@@ -4,18 +4,31 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# Luanch stunnel once and only once. This should never crash, but if it does,
+# everything should die.
 stunnel \
   -p /engine/data/stunnel.pem \
   -P /engine/stunnel.pid \
   -d 25466 -r 25467 -f &
-LD_LIBRARY_PATH=/engine/ /engine/blimp_engine_app \
-  --disable-gpu \
-  --use-remote-compositing \
-  --disable-cached-picture-raster \
-  --blimp-client-token-path=/engine/data/client_token \
-  --android-fonts-path=/engine/fonts \
-  --disable-remote-fonts \
-  $@ &
 
-# Stop execution if either stunnel or blimp_engine_app die.
-wait -n
+# Start (and restart) the engine so long as there hasn't been an error.
+# Currently, the engine can cleanly exit in the event that a conneciton is lost.
+# In these cases, it's safe to restart the engine. However, if either stunnel or
+# the engine exit with a nonzero return code, stop all execution.
+while :; do
+  LD_LIBRARY_PATH=/engine/ /engine/blimp_engine_app \
+    --disable-gpu \
+    --use-remote-compositing \
+    --disable-cached-picture-raster \
+    --blimp-client-token-path=/engine/data/client_token \
+    --android-fonts-path=/engine/fonts \
+    --disable-remote-fonts \
+    $@ &
+
+  # Wait for a process to exit. Bomb out if anything had an error.
+  wait -n  # Returns the exited process's return code.
+  retcode=$?
+  if [ $retcode -ne 0 ]; then
+    exit $retcode
+  fi
+done