Revert "gclient: remove support for From()"

This reverts commit bf72b593a2fac54e0ac7961be2706581ea47f7f9.

Reason for revert: maybe caused outage.

Original change's description:
> gclient: remove support for From()
> 
> This feature appears unused, and removing it will simplify the codebase.
> 
> Bug: 661382
> Change-Id: I545befb2c592eea53c54552018ce2d3dda7670f5
> Reviewed-on: https://chromium-review.googlesource.com/509693
> Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> 

TBR=phajdan.jr@chromium.org,dpranke@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Bug: 661382

Change-Id: I4db9554a0a3a64a3a69908560b6da2a9963518f2
Reviewed-on: https://chromium-review.googlesource.com/512343
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
diff --git a/gclient_utils.py b/gclient_utils.py
index 8fe0c5e..d46dbd1 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -813,7 +813,8 @@
   """Runs a set of WorkItem that have interdependencies and were WorkItem are
   added as they are processed.
 
-  This class manages that all the required dependencies are run
+  In gclient's case, Dependencies sometime needs to be run out of order due to
+  From() keyword. This class manages that all the required dependencies are run
   before running each one.
 
   Methods of this class are thread safe.