[dart2js:dump_info] put version and program info first...

...more consistent sorting of holdings (improves diffing)

Change-Id: I2f2c418edea1f2dec6b8cc26e8058a5e3855ceb2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/271820
Auto-Submit: Kevin Moore <kevmoo@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>

Author: kevmoo

pkg/dart2js_info/lib/json_info_codec.dart

@@ -415,17 +415,30 @@ class AllInfoToJsonConverter extends Converter<AllInfo, Map>
     };
   }
 
-  Map visitDependencyInfo(DependencyInfo info) =>
-      {'id': idFor(info.target).serializedId, 'mask': info.mask};
+  Map visitDependencyInfo(DependencyInfo info) => {
+        'id': idFor(info.target).serializedId,
+        if (info.mask != null) 'mask': info.mask,
+      };
 
   Map _visitAllInfoHolding(AllInfo allInfo) {
     var map = SplayTreeMap<String, List>(compareNatural);
     void helper(CodeInfo info) {
       if (info.uses.isEmpty) return;
-      map[idFor(info).serializedId] = info.uses
-          .map(visitDependencyInfo)
-          .toList()
-        ..sort((a, b) => a['id'].compareTo(b['id']));
+      map[idFor(info).serializedId] =
+          info.uses.map(visitDependencyInfo).toList()
+            ..sort((a, b) {
+              final value = a['id'].compareTo(b['id']);
+              if (value != 0) return value;
+              final aMask = a['mask'] as String?;
+              final bMask = b['mask'] as String?;
+              if (aMask == null) {
+                return bMask == null ? 0 : 1;
+              }
+              if (bMask == null) {
+                return -1;
+              }
+              return aMask.compareTo(bMask);
+            });
     }
 
     allInfo.functions.forEach(helper);
@@ -447,14 +460,14 @@ class AllInfoToJsonConverter extends Converter<AllInfo, Map>
     var jsonHolding = _visitAllInfoHolding(info);
     var jsonDependencies = _visitAllInfoDependencies(info);
     return {
+      'dump_version': isBackwardCompatible ? 5 : info.version,
+      'dump_minor_version': isBackwardCompatible ? 1 : info.minorVersion,
+      'program': info.program!.accept(this),
       'elements': elements,
       'holding': jsonHolding,
       'dependencies': jsonDependencies,
       'outputUnits': info.outputUnits.map((u) => u.accept(this)).toList(),
-      'dump_version': isBackwardCompatible ? 5 : info.version,
       'deferredFiles': info.deferredFiles,
-      'dump_minor_version': isBackwardCompatible ? 1 : info.minorVersion,
-      'program': info.program!.accept(this)
     };
   }