Revert of Remove the id field of inspector_backend since no public caller uses it

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

Index: tools/telemetry/telemetry/core/backends/chrome/inspector_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/inspector_backend.py b/tools/telemetry/telemetry/core/backends/chrome/inspector_backend.py
index 642257161125c80e6ff3de701ed97ef00f8072fa..bd7680c073da3163389ecb311ae6b015ebe2c0e8 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/inspector_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/inspector_backend.py
@@ -74,9 +74,13 @@
   @property
   def url(self):
     for c in self._browser_backend.ListInspectableContexts():
-      if c['id'] == self._context['id']:
+      if c['id'] == self.id:
         return c['url']
     return None
+
+  @property
+  def id(self):
+    return self._context['id']
 
   @property
   def debugger_url(self):