Configure "Mac Builder (dbg)" to build "all".

Will watch for cycle time increases on the CQ bot:
https://luci-milo.appspot.com/p/chromium/builders/luci.chromium.try/mac_chromium_compile_dbg_ng

R=dpranke, erikchen, jbudorick

Bug: 910227
Change-Id: I73f6e5cc18e707aebe6689034a734ee96fbaa97b
Reviewed-on: https://chromium-review.googlesource.com/c/1370949Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615577}

testing/buildbot/chromium.mac.json

@@ -6,6 +6,11 @@
       "pdf_fuzzers"
     ]
   },
+  "Mac Builder (dbg)": {
+    "additional_compile_targets": [
+      "all"
+    ]
+  },
   "Mac10.10 Tests": {
     "gtest_tests": [
       {

testing/buildbot/waterfalls.pyl

@@ -3071,6 +3071,11 @@
           'pdf_fuzzers',
         ],
       },
+      'Mac Builder (dbg)': {
+        'additional_compile_targets': [
+          'all',
+        ],
+      },
       'Mac10.10 Tests': {
         'mixins': [
             'mac_10.10',