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* Fully disables dex merging for library targets, speeding up builds.
* Introduces sharding into incremental installs, dramatically speeding
  up launch times.
  * E.g. instead of ~250 dex files to load, shards into ~25 files.

Bug: 937005, 1016846
Change-Id: I9a206145be196af61e55c4a25dcce3fbceb7190c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1874046
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708295}