Add directory extraction to GN path handling.

Add directory extraction to GN path handling.

Some of the mojo templates want to put generated files in the directory
corresponding to the source file, rather than the directory containing the
BUILD file. Previously, this required putting the BUILD files in the same
directory.

This patch adds the ability to specify the generated file directory
corresponding to the input file in the action_foreach file templates so this
can be expressed naturally.

For parity, it also adds qquerying for this information via get_path_info.

BUG=
R=cjhopman@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=278402

[brettw, 2014-06-18 17:13:38]

Ping?

[cjhopman, 2014-06-18 18:13:30]

lgtm with some small comments about comments

https://codereview.chromium.org/334333005/diff/40001/tools/gn/file_template.cc
File tools/gn/file_template.cc (right):

https://codereview.chromium.org/334333005/diff/40001/tools/gn/file_template.c...
tools/gn/file_template.cc:78: "      path, relative to the build directory. this
us be different than\n"
nit: s/this/This

https://codereview.chromium.org/334333005/diff/40001/tools/gn/file_template.c...
tools/gn/file_template.cc:78: "      path, relative to the build directory. this
us be different than\n"
"this us"? s/us/may or s/us/will maybe?

https://codereview.chromium.org/334333005/diff/40001/tools/gn/file_template.c...
tools/gn/file_template.cc:80: "      different directory than the build.gn file.
if the input path is\n"
s/if/If

https://codereview.chromium.org/334333005/diff/40001/tools/gn/file_template.c...
tools/gn/file_template.cc:87: "      path, relative to the build directory. this
us be different than\n"
capitalization in this paragraph too

https://codereview.chromium.org/334333005/diff/40001/tools/gn/function_get_pa...
File tools/gn/function_get_path_info.cc (right):

https://codereview.chromium.org/334333005/diff/40001/tools/gn/function_get_pa...
tools/gn/function_get_path_info.cc:27: // Returns the directory containing the
input, regardless of whether the input
directory relative to current_dir?

https://codereview.chromium.org/334333005/diff/40001/tools/gn/function_get_pa...
tools/gn/function_get_path_info.cc:36: // Input is a directory.
s/directory/file

[brettw, 2014-06-19 16:50:55]

Committed patchset #5 manually as r278402 (presubmit successful).