Fix usage of depot_tools in containers.

depot_tools w/vpython now seems to require the depot_tools dir
to be on PATH, and also python and curl need to be installed.

  * Creates a new base image that has all the build tools we need for
building Skia: skia-build-tools.
  * Moves skia-release to use that new base image.
  * Moves both the skia-release and wasm builds to use fetch and gclient sync.
  * Changes gcr.io/skia-public/emsdk-base:prod to depend on skia-build-tools.


Bug: skia:993053
Change-Id: Ib6218d8c18dd59d43de84dcf063f204cfc8556d0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248556
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
diff --git a/docker/Makefile b/docker/Makefile
new file mode 100644
index 0000000..37270b9
--- /dev/null
+++ b/docker/Makefile
@@ -0,0 +1,6 @@
+# Build gcr.io/skia-public/skia-build-tools:latest, the image used to compile
+# Skia in Google Cloud Build.
+push-skia-build-tools:
+	docker build -t skia-build-tools ./skia-build-tools
+	docker tag skia-build-tools gcr.io/skia-public/skia-build-tools:latest
+	docker push gcr.io/skia-public/skia-build-tools:latest
\ No newline at end of file