Fix MB config expectations for 'phased' builders.

Some builders have a different set of GN args used within a single
build. These phased builders didn't have very readable expectations.

This should fix that.

Bug: 1117577
Change-Id: I965081c221d3508bb6988d8a1b45f0f387384537
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2458207Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814865}

tools/mb/mb.py

@@ -713,10 +713,12 @@ class MetaBuildWrapper(object):
         if not config:
           continue
         if isinstance(config, dict):
-          args = {
-              k: FlattenConfig(self.configs, self.mixins, v)['gn_args']
-              for k, v in config.items()
-          }
+          # This is a 'phased' builder. Each key in the config is a different
+          # phase of the builder.
+          args = {}
+          for k, v in config.items():
+            args[k] = gn_helpers.FromGNArgs(
+                FlattenConfig(self.configs, self.mixins, v)['gn_args'])
         elif config.startswith('//'):
           args = config
         else:

tools/mb/mb_config_expectations/chromium.linux.json

@@ -36,8 +36,17 @@
     }
   },
   "Deterministic Linux (dbg)": {
-    "goma": "is_debug=true is_component_build=true use_goma=true symbol_level=1",
-    "local": "is_debug=true is_component_build=true symbol_level=1"
+    "goma": {
+      "is_component_build": true,
+      "is_debug": true,
+      "symbol_level": 1,
+      "use_goma": true
+    },
+    "local": {
+      "is_component_build": true,
+      "is_debug": true,
+      "symbol_level": 1
+    }
   },
   "Fuchsia ARM64": {
     "gn_args": {