Properly sequence database setups between symbol store tests.

Without this, it's possible that we'll have two database creations triggered
right after one another without sequencing. For example, if you have a subtest
that creates a SymbolStore but only looks up invalid symbol tables, then the
database is never consulted, and nothing will block on the database creation
being completed.

src/profile-logic/symbol-store.js

@@ -85,6 +85,10 @@ export class SymbolStore {
     this._db = new SymbolStoreDB(`${dbNamePrefix}-symbol-tables`);
   }
 
+  async closeDb() {
+    await this._db.close();
+  }
+
   // Store a symbol table in the database. This is only used for symbol tables
   // and not for partial symbol results. Symbol tables are generated by the
   // geckoProfiler WebExtension API, so these are symbol tables we get from the

src/test/unit/symbol-store.test.js

@@ -40,6 +40,9 @@ describe('SymbolStore', function() {
   });
 
   afterEach(async function() {
+    if (symbolStore) {
+      await symbolStore.closeDb().catch(() => {});
+    }
     await deleteDatabase();
   });
 
@@ -137,12 +140,10 @@ describe('SymbolStore', function() {
     // Using another symbol store simulates a page reload
     // Due to https://github.com/dumbmatter/fakeIndexedDB/issues/22 we need to
     // take care to sequence the DB open requests.
-    const symbolStore2 = new SymbolStore(
-      'perf-html-async-storage',
-      symbolProvider
-    );
+    await symbolStore.closeDb().catch(() => {});
+    symbolStore = new SymbolStore('perf-html-async-storage', symbolProvider);
 
-    await symbolStore2.getSymbols(
+    await symbolStore.getSymbols(
       [{ lib: lib, addresses: new Set([0x1]) }],
       (_request, _results) => {},
       (_request, _error) => {}