Bump usage to ac53249e5230a77624f46c07c2ed965efcfc0c59

This is a reland of: https://dart-review.googlesource.com/c/sdk/+/213349
Reverted in https://dart-review.googlesource.com/c/sdk/+/213440 due to http://b/199988795

The two failures in that issue has been addressed by "ac53249 Fix timeout" and "117d3a1 Allow sendRaw to send Map<String, dynamic>"


Most of these commits stem from a non-squashed merge.

Changes:
```
> git log --format="%C(auto) %h %s" e0780cd..ac53249
 https://dart.googlesource.com/usage.git/+/ac53249 Fix timeout (#162)
 https://dart.googlesource.com/usage.git/+/117d3a1 Allow sendRaw to send Map<String, dynamic> (#161)
 https://dart.googlesource.com/usage.git/+/016dd30 Prepare release (#160)
 https://dart.googlesource.com/usage.git/+/076c653 Merge pull request #152 from sigurdm/batching
 https://dart.googlesource.com/usage.git/+/1d6b343 Remove debug print
 https://dart.googlesource.com/usage.git/+/c073fb7 Use correct limit for bytes
 https://dart.googlesource.com/usage.git/+/1d89875 Send batch early if full
 https://dart.googlesource.com/usage.git/+/2896a85 Update README.md
 https://dart.googlesource.com/usage.git/+/da20fab Delete travis.sh
 https://dart.googlesource.com/usage.git/+/7c351a3 Merge
 https://dart.googlesource.com/usage.git/+/0424091 Update build.yaml (#159)
 https://dart.googlesource.com/usage.git/+/4f2a050 Use a Duration for batching delay
 https://dart.googlesource.com/usage.git/+/aa3f3ce address review
 https://dart.googlesource.com/usage.git/+/318ebe5 Fix
 https://dart.googlesource.com/usage.git/+/71ddec1 Send remaining hits on waitForLastPing
 https://dart.googlesource.com/usage.git/+/1c895a7 Parametrize client-id in test
 https://dart.googlesource.com/usage.git/+/0ae7733 Fix pubspec
 https://dart.googlesource.com/usage.git/+/2255b3d Merge remote-tracking branch 'origin/master' into batching
 https://dart.googlesource.com/usage.git/+/14d3702 Merge remote-tracking branch 'origin/master' into batching
 https://dart.googlesource.com/usage.git/+/1c3393d Handle batching implicit waiting for a 'batchDelay' future
 https://dart.googlesource.com/usage.git/+/219b764 TODO about size of payloads
 https://dart.googlesource.com/usage.git/+/aaee6d9 Fix AnalyticsMock
 https://dart.googlesource.com/usage.git/+/a8ec5b4 Remove mockito as dep - didn't use it
 https://dart.googlesource.com/usage.git/+/e26fcce Allow batching of hits

```

Diff: https://dart.googlesource.com/usage.git/+/e0780cd8b2f8af69a28dc52678ffe8492da27d06~..ac53249e5230a77624f46c07c2ed965efcfc0c59/
Change-Id: I1284db2a23a3e9ac037d1d2a80627c0caa1e9385
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/216184
Reviewed-by: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>

DEPS

@@ -163,7 +163,7 @@ vars = {
   "test_reflective_loader_rev": "fcfce37666672edac849d2af6dffc0f8df236a94",
   "test_rev": "099dcc4d052a30c6921489cfbefa1c8531d12975",
   "typed_data_rev": "29ce5a92b03326d0b8035916ac04f528874994bd",
-  "usage_rev": "e0780cd8b2f8af69a28dc52678ffe8492da27d06",
+  "usage_rev": "ac53249e5230a77624f46c07c2ed965efcfc0c59",
   "vector_math_rev": "0c9f5d68c047813a6dcdeb88ba7a42daddf25025",
   "watcher_rev": "3924194385fb215cef483193ed2879a618a3d69c",
   "webdriver_rev": "ff5ccb1522edf4bed578ead4d65e0cbc1f2c4f02",