Revert "Android: Remove obsolete comments in javac.py"

This reverts commit bf48f734.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 723529 as the
culprit for failures in the build cycles as shown on:
https://analysis.chromium.org/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtL2JmNDhmNzM0MGJmN2QwY2NiMjg4MmNjZDI2MmRmMTE3YWJhNmJiM2EM

Sample Failed Build: https://ci.chromium.org/b/8894421463503746800

Sample Failed Step: compile

Original change's description:
> Android: Remove obsolete comments in javac.py
> 
> Now that we have migrated to using the javac binary in third_party/jdk
> and only turning on the errorprone plugin when it is enabled, we no
> longer need this comment.
> 
> Bug: 1030676
> Change-Id: I27a3d8ea19da698fa74e869fdcd878ca922956c1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959901
> Commit-Queue: Peter Wen <wnwen@chromium.org>
> Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> Auto-Submit: Peter Wen <wnwen@chromium.org>
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#723529}


Change-Id: Ieaa827f4029ddc0154ab848e3f7f12e0f17e3dd5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1030676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1961065
Cr-Commit-Position: refs/heads/master@{#723552}

build/android/gyp/javac.py

@@ -524,6 +524,14 @@ def main(argv):
 
   argv = build_utils.ExpandFileArgs(argv)
   options, java_files = _ParseOptions(argv)
+
+  # Until we add a version of javac via DEPS, use errorprone with all checks
+  # disabled rather than javac. This ensures builds are reproducible.
+  # https://crbug.com/693079
+  # As of Jan 2019, on a z920, compiling chrome_java times:
+  # * With javac: 17 seconds
+  # * With errorprone (checks disabled): 20 seconds
+  # * With errorprone (checks enabled): 30 seconds
   javac_path = build_utils.JAVA_PATH + 'c'
 
   javac_cmd = [