Add section for SafeBrowsingUpdateFrequency in fieldtrial on win/mac/linux

testing/variations/fieldtrial_testing_config_linux.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 95 matching lines @@
         {
             "group_name": "Enabled"
         },
         {
             "group_name": "Control"
         },
         {
             "group_name": "Disabled"
         }
     ],
+    "SafeBrowsingUpdateFrequency": [
+        {
+            "group_name": "Control"
+        },
+        {
+            "group_name": "Default"
+        },
+        {
+            "group_name": "UpdateTime15m"

[Nathan Parker, 2015/12/04 21:41:05]

You also need the param here to set it to 15 minutes.

I heard that currently only the first in this list is tested... in case that's
still try, put the "15m" one first since that affects the most new code.  Same
in other files.

[vakh (old account. dont use), 2015/12/08 19:25:32]

Done.

+        }
+    ],
     "SdchPersistence": [
         {
             "group_name": "Enabled"
         }
     ],
     "SyncHttpContentCompression": [
         {
             "group_name": "Enabled"
         },
         {
@@ skipping 22 matching lines @@
         {
             "group_name": "Enabled"
         }
     ],
     "WebRTC-PeerConnectionDTLS1.2": [
         {
             "group_name": "Enabled"
         }
     ]
 }