Replace 10.7 testers with 10.9 in master.chromium.mac

masters/master.chromium.mac/slaves.cfg

Index: masters/master.chromium.mac/slaves.cfg
diff --git a/masters/master.chromium.mac/slaves.cfg b/masters/master.chromium.mac/slaves.cfg
index 86ead24dca74c7d70be68d27339d6e7473bb340a..ef69c4291fc8dd5da82efaac1dbe5a8984868245 100644
--- a/masters/master.chromium.mac/slaves.cfg
+++ b/masters/master.chromium.mac/slaves.cfg
@@ -23,9 +23,9 @@ slaves = [
   {
     'master': 'ChromiumMac',
     'hostname': 'vm600-m1',
-    'builder': 'Mac10.7 Tests (1)',
+    'builder': 'Mac10.9 Tests (1)',
     'os': 'mac',
-    'version': '10.7',
+    'version': '10.9',
     'bits': '64',
   },
   {
@@ -47,9 +47,9 @@ slaves = [
   {
     'master': 'ChromiumMac',
     'hostname': 'vm11-a1',
-    'builder': 'Mac 10.7 Tests (dbg)(1)',
+    'builder': 'Mac 10.9 Tests (dbg)(1)',
     'os': 'mac',
-    'version': '10.7',
+    'version': '10.9',
     'bits': '64',
   },
   {