Modified python agent to include the request log id into the breakpoint labels for GAE Classic applications only.

This is a re-submit of cl/125829312 that was rolled back.
It should work now that we checked in the modified serializer to/from json/protobuf[2|3].

I will send another CL for the updated aeta python test, i prefer having the test get in into a separate CL (so that @emrekultursay can run the plain test the day after we check in against nightly and also the updated one).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130292452

Author: dragoluigi

src/googleclouddebugger/capture_collector.py

@@ -24,6 +24,7 @@
 import sys
 import types
 
+import labels
 import cdbg_native as native
 
 # Externally defined functions to actually log a message. If these variables
@@ -32,6 +33,9 @@
 log_warning_message = None
 log_error_message = None
 
+# Externally defined function to collect the request log id.
+request_log_id_collector = None
+
 _PRIMITIVE_TYPES = (int, long, float, complex, str, unicode, bool,
                     types.NoneType)
 _DATE_TYPES = (datetime.date, datetime.time, datetime.timedelta)
@@ -164,6 +168,8 @@ def Collect(self, top_frame):
     # didn't make it point to var_index of 0 ("buffer full")
     self.TrimVariableTable(i)
 
+    self._CaptureRequestLogId()
+
   def CaptureFrameLocals(self, frame):
     """Captures local variables and arguments of the specified frame.
 
@@ -381,6 +387,22 @@ def ProcessBufferFull(variables):
     ProcessBufferFull(self._var_table)
     ProcessBufferFull(self.breakpoint['evaluatedExpressions'])
 
+  def _CaptureRequestLogId(self):
+    """Captures the request log id if possible.
+
+    The request log id is stored inside the breakpoint labels.
+    """
+    # pylint: disable=not-callable
+    if callable(request_log_id_collector):
+      request_log_id = request_log_id_collector()
+      if request_log_id:
+        # We have a request_log_id, save it into the breakpoint labels
+        if 'labels' not in self.breakpoint:
+          self.breakpoint['labels'] = {}
+
+        self.breakpoint['labels'][
+            labels.Breakpoint.REQUEST_LOG_ID] = request_log_id
+
   @staticmethod
   def _NormalizePath(path):
     """Converts an absolute path to a relative one.