Add Dependency.hierarchy() to better visualize the origin of a dependency.

Add Dependency.hierarchy() to better visualize the origin of a dependency.

TBR=bradnelson

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=53379

[M-A Ruel, 2010-07-22 20:58:12]

It gives a better idea of what is going wrong in the code. No code change in the
normal flow.

________ running 'svn update ..src/pagespeed/src' in '..src/pagespeed'
At revision 980.
Syncing projects:  17% (4/23)  Error: Dependency src/googleurl specified more
than once:
  src(http://page-speed.googlecode.com/svn/lib/trunk/src) ->
src/googleurl(From('src/third_party/chromium_deps', None))
vs
  src(http://page-speed.googlecode.com/svn/lib/trunk/src) ->
src/third_party/chromium_deps(File("http://src.chromium.org/svn/trunk/src/DEPS@50096"))
-> src/googleurl(http://google-url.googlecode.com/svn/trunk@134)

[bradn, 2010-07-22 21:22:25]

http://codereview.chromium.org/2883035/diff/2001/3001
File gclient.py (right):

http://codereview.chromium.org/2883035/diff/2001/3001#newcode442
gclient.py:442: "Returns a human-readable hierarchical reference to a
Dependency."
Uh you'll want a """ here I believe.