Autoroller: Support for rolling individual DEPS entries.

tools/autoroller/unittests/testdata/DEPS.chromium.new

Index: tools/autoroller/unittests/testdata/DEPS.chromium.new
diff --git a/tools/autoroller/unittests/testdata/DEPS.chromium.new b/tools/autoroller/unittests/testdata/DEPS.chromium.new
new file mode 100644
index 0000000000000000000000000000000000000000..d53083ceec5e79c5757f12f79d69cd18a53d09e3
--- /dev/null
+++ b/tools/autoroller/unittests/testdata/DEPS.chromium.new
@@ -0,0 +1,13 @@
+# DEPS file for unit tests.
+
+vars = {
+  'chromium_git': 'https://chromium.googlesource.com',
+
+  # This is updated compared to the DEPS.chromium.old file.
+  'buildtools_revision': '55ad626b08ef971fd82a62b7abb325359542952b',
+}
+
+deps = {
+  'src/buildtools':
+    Var('chromium_git') + '/chromium/buildtools.git' + '@' +  Var('buildtools_revision'),
+}