Factoring out device affinity generation to be used in swarming

telemetry/telemetry/benchmark_runner.py

Index: telemetry/telemetry/benchmark_runner.py
diff --git a/telemetry/telemetry/benchmark_runner.py b/telemetry/telemetry/benchmark_runner.py
index 3828bad16db2fd99cd99949992eba94926e5cd7d..a3387d72c4aede1549172245469e194a4f8a6812 100644
--- a/telemetry/telemetry/benchmark_runner.py
+++ b/telemetry/telemetry/benchmark_runner.py
@@ -8,7 +8,6 @@ Handles benchmark configuration, but all the logic for
 actually running the benchmark is in Benchmark and PageRunner."""
 
 import argparse
-import hashlib
 import json
 import logging
 import os
@@ -23,6 +22,7 @@ from telemetry.internal.util import binary_manager
 from telemetry.internal.util import command_line
 from telemetry.internal.util import ps_util
 from telemetry.util import matching
+from telemetry.util import bot_utils
 
 
 # Right now, we only have one of each of our power perf bots. This means that
@@ -358,18 +358,7 @@ def _GetJsonBenchmarkList(possible_browser, possible_reference_browser,
                 base_name]
     perf_dashboard_id = base_name
 
-    # Based on the current timings, we shift the result of the hash function to
-    # achieve better load balancing. Those shift values are to be revised when
-    # necessary. The shift value is calculated such that the total cycle time
-    # is minimized.
-    hash_shift = {
-      2 : 47,  # for old desktop configurations with 2 slaves
-      5 : 56,  # for new desktop configurations with 5 slaves
-      21 : 43  # for Android 3 slaves 7 devices configurations
-    }
-    shift = hash_shift.get(num_shards, 0)
-    base_name_hash = hashlib.sha1(base_name).hexdigest()
-    device_affinity = (int(base_name_hash, 16) >> shift) % num_shards
+    device_affinity = bot_utils.GetDeviceAffinity(num_shards, base_name)
 
     output['steps'][base_name] = {
       'cmd': ' '.join(base_cmd + [