Create a Dockerfile.base and ensure it is included in build tarballs.

blimp/tools/Dockerfile.base

Index: blimp/tools/Dockerfile.base
diff --git a/blimp/engine/Dockerfile b/blimp/tools/Dockerfile.base
similarity index 58%
copy from blimp/engine/Dockerfile
copy to blimp/tools/Dockerfile.base
index 745c12de93b625b57ad1955df92bf37f9ebdaa20..eefd0b44978d342cffb326b3a0049bf9e4b1a29c 100644
--- a/blimp/engine/Dockerfile
+++ b/blimp/tools/Dockerfile.base
@@ -1,3 +1,5 @@
+# Blimp base Dockerfile. Should be used by all Dockerfiles used by Blimp to
+# ensure test and release binaries all run under the same system environment.
 FROM ubuntu:trusty
 
 # Run the command below to update the lib list.
@@ -13,20 +15,4 @@ RUN apt-get update && apt-get install -yq stunnel4 wget
 
 # gdb and strace are not strictly required, but having them around makes
 # debugging easier.
-RUN apt-get update && apt-get install -yq gdb strace
-

[Sriram, 2016/06/16 18:04:08]

Do we need a todo in blimp/engine/Dockerfile to use Dockerfile.base at later
point?

[Jess, 2016/06/16 18:18:11]

I didn't worry about it given the tracking bug http://crbug/616945 . Honestly
was expecting this change to take less than a day to commit and be getting that
follow up in by today. :)

-RUN mkdir /engine
-
-RUN useradd -ms /bin/bash blimp_user
-
-# The glob below expands to all files, but does not add directories
-# recursively.
-ADD * /engine/
-ADD gen/third_party/blimp_fonts /engine/fonts
-RUN mv /engine/chrome_sandbox /engine/chrome-sandbox
-RUN chown -R blimp_user /engine
-
-USER blimp_user
-WORKDIR "/engine"
-
-ENTRYPOINT ["/engine/start_engine.sh"]
+RUN apt-get update && apt-get install -yq gdb strace