[Telemetry] Factor out common logic between inspector backend lists.

tools/telemetry/telemetry/core/backends/chrome/inspector_backend_list.py

Index: tools/telemetry/telemetry/core/backends/chrome/inspector_backend_list.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/inspector_backend_list.py b/tools/telemetry/telemetry/core/backends/chrome/inspector_backend_list.py
new file mode 100644
index 0000000000000000000000000000000000000000..119c2df6c14c7e754430114984d93ff33288b8b9
--- /dev/null
+++ b/tools/telemetry/telemetry/core/backends/chrome/inspector_backend_list.py
@@ -0,0 +1,85 @@
+# Copyright 2014 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 collections
+import json
+
+from telemetry.core.backends.chrome import inspector_backend
+
+
+def DebuggerUrlToId(debugger_url):
+  return debugger_url.split('/')[-1]
+
+
+class InspectorBackendList(collections.Sequence):
+  """A dynamic sequence of active InspectorBackends."""
+
+  def __init__(self, browser_backend, backend_wrapper=None):
+    """Constructor.
+
+    Args:
+      browser_backend: The BrowserBackend instance to query for
+          InspectorBackends.
+      backend_wrapper: A public interface for wrapping each
+          InspectorBackend. It must accept a single argument of the
+          InspectorBackend to wrap and may expose whatever methods
+          are desired on top of that backend.
+    """
+    self._browser_backend = browser_backend
+    # A ordered mapping of context IDs to inspectable contexts.
+    self._inspectable_contexts_dict = collections.OrderedDict()
+    # A cache of inspector backends, by context ID.
+    self._inspector_backend_dict = {}
+    # A wrapper class for InspectorBackends.
+    self._backend_wrapper = backend_wrapper
+
+  def GetContextInfo(self, context_id):
+    return self._inspectable_contexts_dict[context_id]
+
+  def ShouldIncludeContext(self, _context):
+    """Override this method to control which contexts are included."""
+    return True
+
+  def __getitem__(self, index):
+    self._Update()
+    context_id = self._inspectable_contexts_dict.keys()[index]
+    if context_id not in self._inspector_backend_dict:
+      backend = inspector_backend.InspectorBackend(
+          self._browser_backend.browser,
+          self._browser_backend,
+          self._inspectable_contexts_dict[context_id])
+      if self._backend_wrapper:
+        backend = self._backend_wrapper(backend)
+      self._inspector_backend_dict[context_id] = backend
+    return self._inspector_backend_dict[context_id]
+
+  def __iter__(self):
+    self._Update()
+    return self._inspectable_contexts_dict.keys().__iter__()
+
+  def __len__(self):
+    self._Update()
+    return len(self._inspectable_contexts_dict)
+
+  def _Update(self):
+    contexts = json.loads(self._browser_backend.Request(''))
+    context_ids = [context['id'] for context in contexts]
+
+    # Append all new inspectable contexts to the dict.
+    for context in contexts:
+      if not self.ShouldIncludeContext(context):
+        continue
+      if context['id'] in self._inspectable_contexts_dict:
+        continue
+      self._inspectable_contexts_dict[context['id']] = context
+
+    # Remove all inspectable contexts that have gone away from the dict.
+    for context_id in self._inspectable_contexts_dict.keys():
+      if context_id not in context_ids:
+        del self._inspectable_contexts_dict[context_id]
+
+    # Clean up any backends for contexts that have gone away.
+    for context_id in self._inspector_backend_dict.keys():
+      if context_id not in self._inspectable_contexts_dict:
+        del self._inspector_backend_dict[context_id]