Add a recipe to identify culprits for chromium compile failures.

scripts/slave/recipe_modules/findit/api.py

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+from recipe_engine import recipe_api
+
+
+class FinditApi(recipe_api.RecipeApi):
+
+  def _calculate_repo_dir(self, solution_name):
+    """Returns the relative path of the solution checkout to the root one."""
+    if solution_name == 'src':
+      return ''
+    else:
+      root_solution_name = 'src/'
+      assert solution_name.startswith(root_solution_name)
+      return solution_name[len(root_solution_name):]
+
+  def get_files_affected_by_revision(self, revision, solution_name):
+    """Returns the files changed by the given revision.

[Dirk Pranke, 2015/11/24 00:17:41]

I would probably call this routine "files_changed_by_revision" (or maybe
files_changed_in_revision).

We don't generally want to call things "get_X" in chromium style, just "X", and
"changed" is probably 
a bit clearer than "affected" in this context.

[stgao, 2015/11/24 23:19:19]

Done.

+
+    Args:
+      revision (str): the git hash of a commit.
+      solution_name (str): the gclient solution name, eg:
+          "src" for chromium, "src/third_party/pdfium" for pdfium.
+    """
+    solution_name = solution_name.replace('\\', '/')
+    repo_dir = self._calculate_repo_dir(solution_name)
+    cwd = self.m.path['checkout'].join(repo_dir)
+
+    previous_revision = '%s~1' % revision
+    step_result = self.m.git('diff', revision + '~1', revision, '--name-only',
+                             name='git diff to analyze commit',
+                             stdout=self.m.raw_io.output(),
+                             cwd=cwd,
+                             step_test_data=lambda:
+                             self.m.raw_io.test_api.stream_output('foo.cc'))
+
+    paths = step_result.stdout.split()
+    if repo_dir:
+      paths = [self.m.path.join(repo_dir, path) for path in paths]
+    if self.m.platform.is_win:
+      # Looks like "analyze" wants POSIX slashes even on Windows (since git
+      # uses that format even on Windows).
+      paths = [path.replace('\\', '/') for path in paths]
+
+    step_result.presentation.logs['files'] = paths
+    return paths