NaCl: Allow download_nacl_irt.py to be usefully invoked with no arguments

Extend the script to read the NaCl revisions/hashes directly from DEPS
in this case.

This makes the script usable in cases where you don't want to run
"gclient runhooks", such as when creating a tarball of the checkout,
in which case it is not desirable to run Gyp and have it generate
makefiles.

Admittedly this is redundant, because it adds a second way of getting
information from DEPS to the download_nacl_irt.py script.

The implementation of EvalDepsFile() is borrowed from:
http://src.chromium.org/viewvc/native_client/trunk/src/native_client/build/chromebinaries.py?revision=4577&view=markup

BUG=http://bugs.gentoo.org/show_bug.cgi?id=366413
TEST=run "python src/build/download_nacl_irt.py"

Review URL: http://codereview.chromium.org/6966010

git-svn-id: http://src.chromium.org/svn/trunk/src/build@84863 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

download_nacl_irt.py

@@ -119,6 +119,12 @@ def DownloadFileWithRetry(dest_path, url):
       time.sleep(1)
 
 
+def EvalDepsFile(path):
+  scope = {'Var': lambda name: scope['vars'][name]}
+  execfile(path, {}, scope)
+  return scope
+
+
 def Main():
   parser = optparse.OptionParser()
   parser.add_option(
@@ -143,6 +149,18 @@ def Main():
   if len(args) != 0:
     parser.error('Unexpected arguments: %r' % args)
 
+  if options.nacl_revision is None and len(options.file_hashes) == 0:
+    # The script must have been invoked directly with no arguments,
+    # rather than being invoked by gclient.  In this case, read the
+    # DEPS file ourselves rather than having gclient pass us values
+    # from DEPS.
+    deps_data = EvalDepsFile(os.path.join('src', 'DEPS'))
+    options.nacl_revision = deps_data['vars']['nacl_revision']
+    options.file_hashes = [
+        ('x86_32', deps_data['vars']['nacl_irt_hash_x86_32']),
+        ('x86_64', deps_data['vars']['nacl_irt_hash_x86_64']),
+        ]
+
   nacl_dir = os.path.join('src', 'native_client')
   if not os.path.exists(nacl_dir):
     # If "native_client" is not present, this might be because the