Merge from goog/master.
The following CLs are included in this merge:
dc873fa Fix test_http_server location.
f285857 Implement suspend, resume and cancel the download.
14dbd33 Mount the new system as 'postinstall_file' in postinstall.
390efed Parse postinstall parameters from the payload metadata.
14fd1ec Allow to Suspend/Resume the ActionProcessor.
f25eb49 Fix resuming canceled updates.
4eccae2 Fix unittest compile
63bdd87 Don't rebuild .img files on incremental builds.
c90be63 Fix Ext2FilesystemTest unittests on Brillo.
bffa060 Fix *ExtentWriterTest unittest.
279bbab Fix Subprocess unittests.
5fe0c4e Fix unittest build in x86_64.
80f70ff Build unittests in Brillo.
b3f699a Add .clang-format symlink to Brillo's clang-format.
0cd976d Disable ChromeBrowserProxyResolver behind a flag.
71102a2 Fix unittest build.
a96ddc1 Define libupdate_engine_client before using it.
2997173 Add a feature to get the last UpdateAttempt ErrorCode from update_engine
While unittests changes are not compiled in nyc-dev, this helps
cherry-pick of CLs that modify the code and the unittests in the
future without extra risk for nyc-dev.
Bug: 24277309
Bug: 25598547
Bug: 26955860
Bug: 27047026
Bug: 27121653
Bug: 27177071
TEST=`make dist` in nyc-dev
Change-Id: I023f35d4187650ce6cd1e9e3acbdda74ef8a36ea