Add embedded font assets to the asset list

Any font asset referenced in the fonts section of flutter.yaml will now be
included in the FLX assets.  It's no longer necessary to separately list the
font in the assets section.

packages/flutter_tools/lib/src/flx.dart

@@ -81,6 +81,23 @@ Map<_Asset, List<_Asset>> _parseAssets(Map<String, dynamic> manifestDescriptor,
       }
     }
   }
+
+  // Add assets referenced in the fonts section of the manifest.
+  if (manifestDescriptor.containsKey('fonts')) {
+    for (Map<String, dynamic> family in manifestDescriptor['fonts']) {
+      List<Map<String, dynamic>> fonts = family['fonts'];
+      if (fonts == null) continue;
+
+      for (Map<String, dynamic> font in fonts) {
+        String asset = font['asset'];
+        if (asset == null) continue;
+
+        _Asset baseAsset = new _Asset(base: assetBase, key: asset);
+        result[baseAsset] = <_Asset>[];
+      }
+    }
+  }
+
   return result;
 }