Reland of Fix javac command never caching input .md5s

Reland of Fix javac command never caching input .md5s (patchset #1 id:1 of https://codereview.chromium.org/1309663005/ )

Reason for revert:
Fixed the issue.

Original issue's description:
> Revert of Fix javac command never caching input .md5s (patchset #8 id:140001 of https://codereview.chromium.org/1308083002/ )
>
> Reason for revert:
> Causing try-bot failures:
>
> e.g.: http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromium_gn_compile_dbg/builds/111130/steps/compile%20%28without%20patch%29/logs/stdio
>
> Original issue's description:
> > Fix javac command never caching input .md5s
> >
> > This was broken over a year ago by http://crrev.com/a78eb479
> >
> > This change also removes --classes-dir (which is currently unused), and makes --jar-path (always used) required.
> >
> > It also forces the command to run if the output is missing (rather than relying completely on the .stamp file)
> >
> > On my ubiquity machine:
> > Add a log statement to a file in base_java then build chrome_apk:
> >
> > Before:
> > real    2m25.188s
> > user    4m52.950s
> > sys     1m10.064s
> >
> > After:
> > real    1m16.989s
> > user    1m13.795s
> > sys     0m44.040s
> >
> > BUG=523420, 379190
> >
> > Committed: https://crrev.com/1c366880cb68fbf25050f1c6d78684eb6ae2e644
> > Cr-Commit-Position: refs/heads/master@{#346975}
>
> TBR=jbudorick@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=523420, 379190
>
> Committed: https://crrev.com/a936d4429436bd69009eecdc8a8fa97763dcbe22
> Cr-Commit-Position: refs/heads/master@{#347011}

TBR=jbudorick@chromium.org
BUG=523420, 379190
Committed: https://crrev.com/3c8168f5a9168267569eba6bc0b21b0da592d29d
Cr-Commit-Position: refs/heads/master@{#347037}

[agrieve, 2015-09-02 20:41:31]

Created Reland of Fix javac command never caching input .md5s

[agrieve, 2015-09-02 20:45:11]

The CQ bit was checked by agrieve@chromium.org

[commit-bot: I haz the power, 2015-09-02 20:45:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1324203002/120001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1324203002/120001

[jbudorick, 2015-09-02 20:47:47]

lgtm

[commit-bot: I haz the power, 2015-09-02 22:02:31]

Committed patchset #2 (id:120001)

[commit-bot: I haz the power, 2015-09-02 22:03:02]

Patchset 2 (id:??) landed as
https://crrev.com/3c8168f5a9168267569eba6bc0b21b0da592d29d
Cr-Commit-Position: refs/heads/master@{#347037}