Bug 1175942 - Move linux 64 dbg builds to the debug line in treeherder; r=dustin

--HG--
extra : rebase_source : 979becf14818fd9e1d3d167faf4eb91198ef95f3

testing/taskcluster/tasks/builds/dbg_linux64.yml

@@ -13,3 +13,10 @@ task:
   payload:
     env:
       MH_CUSTOM_BUILD_VARIANT_CFG: 'debug'
+  extra:
+    treeherder:
+      groupSymbol: tc
+      groupName: Submitted by taskcluster
+      symbol: B
+      collection:
+        debug: true