Add support for caching results of shared modules.

This is important as we will soon add support for compiling the sdk as a
module and we would like to only compile it once when running a suite of
tests.

+ also enable caching in the dart2js pipeline test.

Change-Id: Ic9043f868123164f3ab425ba73f7428416b05fc0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103485
Commit-Queue: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

https://dart.googlesource.com/sdk/+/edadc9c88149b52bb090dd2cc12de4e3fafb7640
diff --git a/commits.json b/commits.json
index 377267d..cf7b130 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"ee6a9c40492e54a0ae160293900d9e3b42b725d7",
   "external/github.com/flutter/flutter":"1bd85dd6c207d69c148b92ec8f68244c00dec503",
-  "sdk":"8208e872f829e71b7e2eb2953f08515e30b20e0a"
+  "sdk":"edadc9c88149b52bb090dd2cc12de4e3fafb7640"
 }
\ No newline at end of file