[snapshot] support multiple contexts in the same snapshot.

test/memory/Memory.json

Index: test/memory/Memory.json
diff --git a/test/memory/Memory.json b/test/memory/Memory.json
index 1cdc1487c4499df4e0f36c531eca2a6c9d5b2c85..c6b8cd50a2b3abb63d40ba21227cb636584eaa0e 100644
--- a/test/memory/Memory.json
+++ b/test/memory/Memory.json
@@ -12,7 +12,7 @@
     },
     {
       "name": "ReservedMemoryContext",
-      "results_regexp": "(\\d+) bytes per context$"
+      "results_regexp": "(\\d+) bytes per context #0$"
     },
     {
       "name": "SnapshotSizeStartup",
@@ -20,7 +20,7 @@
     },
     {
       "name": "SnapshotSizeContext",
-      "results_regexp": "(\\d+) bytes for context$"
+      "results_regexp": "(\\d+) bytes for context #0$"
     }
   ]
 }