Update from https://crrev.com/304121

build/android/pylib/base/test_collection.py

Index: build/android/pylib/base/test_collection.py
diff --git a/build/android/pylib/base/test_collection.py b/build/android/pylib/base/test_collection.py
new file mode 100644
index 0000000000000000000000000000000000000000..e914652a2a32add3371144222851b47f13918f69
--- /dev/null
+++ b/build/android/pylib/base/test_collection.py
@@ -0,0 +1,80 @@
+# Copyright 2013 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.
+
+import threading
+
+class TestCollection(object):
+  """A threadsafe collection of tests.
+
+  Args:
+    tests: List of tests to put in the collection.
+  """
+
+  def __init__(self, tests=None):
+    if not tests:
+      tests = []
+    self._lock = threading.Lock()
+    self._tests = []
+    self._tests_in_progress = 0
+    # Used to signal that an item is available or all items have been handled.
+    self._item_available_or_all_done = threading.Event()
+    for t in tests:
+      self.add(t)
+
+  def _pop(self):
+    """Pop a test from the collection.
+
+    Waits until a test is available or all tests have been handled.
+
+    Returns:
+      A test or None if all tests have been handled.
+    """
+    while True:
+      # Wait for a test to be available or all tests to have been handled.
+      self._item_available_or_all_done.wait()
+      with self._lock:
+        # Check which of the two conditions triggered the signal.
+        if self._tests_in_progress == 0:
+          return None
+        try:
+          return self._tests.pop(0)
+        except IndexError:
+          # Another thread beat us to the available test, wait again.
+          self._item_available_or_all_done.clear()
+
+  def add(self, test):
+    """Add an test to the collection.
+
+    Args:
+      test: A test to add.
+    """
+    with self._lock:
+      self._tests.append(test)
+      self._item_available_or_all_done.set()
+      self._tests_in_progress += 1
+
+  def test_completed(self):
+    """Indicate that a test has been fully handled."""
+    with self._lock:
+      self._tests_in_progress -= 1
+      if self._tests_in_progress == 0:
+        # All tests have been handled, signal all waiting threads.
+        self._item_available_or_all_done.set()
+
+  def __iter__(self):
+    """Iterate through tests in the collection until all have been handled."""
+    while True:
+      r = self._pop()
+      if r is None:
+        break
+      yield r
+
+  def __len__(self):
+    """Return the number of tests currently in the collection."""
+    return len(self._tests)
+
+  def test_names(self):
+    """Return a list of the names of the tests currently in the collection."""
+    with self._lock:
+      return list(t.test for t in self._tests)