Add predictable mode to test driver.

tools/testrunner/objects/context.py

Index: tools/testrunner/objects/context.py
diff --git a/tools/testrunner/objects/context.py b/tools/testrunner/objects/context.py
index d288e0e05304eab99acb1fd870968f0b1d1e256e..937d9089f35347bc18bd164535982b6298096621 100644
--- a/tools/testrunner/objects/context.py
+++ b/tools/testrunner/objects/context.py
@@ -29,7 +29,8 @@
 class Context():
   def __init__(self, arch, mode, shell_dir, mode_flags, verbose, timeout,
                isolates, command_prefix, extra_flags, noi18n, random_seed,
-               no_sorting, rerun_failures_count, rerun_failures_max):
+               no_sorting, rerun_failures_count, rerun_failures_max,
+               predictable):
     self.arch = arch
     self.mode = mode
     self.shell_dir = shell_dir
@@ -44,16 +45,17 @@ class Context():
     self.no_sorting = no_sorting
     self.rerun_failures_count = rerun_failures_count
     self.rerun_failures_max = rerun_failures_max
+    self.predictable = predictable
 
   def Pack(self):
     return [self.arch, self.mode, self.mode_flags, self.timeout, self.isolates,
             self.command_prefix, self.extra_flags, self.noi18n,
             self.random_seed, self.no_sorting, self.rerun_failures_count,
-            self.rerun_failures_max]
+            self.rerun_failures_max, self.predictable]
 
   @staticmethod
   def Unpack(packed):
     # For the order of the fields, refer to Pack() above.
     return Context(packed[0], packed[1], None, packed[2], False,
                    packed[3], packed[4], packed[5], packed[6], packed[7],
-                   packed[8], packed[9], packed[10], packed[11])
+                   packed[8], packed[9], packed[10], packed[11], packed[12])