Bug 1342051 - clear css grid pattern cache when destroying highlighter;r=zer0

MozReview-Commit-ID: 5LpjjzjZfs3

--HG--
extra : rebase_source : f23974994ff8d10b61e4b6f79dffb69eb985822a

devtools/client/inspector/rules/test/browser_rules_grid-highlighter-on-reload.js

@@ -30,7 +30,7 @@ add_task(function* () {
   let target = TargetFactory.forTab(gBrowser.selectedTab);
   yield gDevTools.closeToolbox(target);
 
-  refreshTab(gBrowser.selectedTab);
+  yield refreshTab(gBrowser.selectedTab);
 
   info("Check that the grid highlighter can be displayed after reloading the page");
   yield checkGridHighlighter();

devtools/server/actors/highlighters/css-grid.js

@@ -241,6 +241,9 @@ CssGridHighlighter.prototype = extend(AutoRefreshHighlighter.prototype, {
     pageListenerTarget.removeEventListener("pagehide", this.onPageHide);
 
     this.markup.destroy();
+
+    // Clear the pattern cache to avoid dead object exceptions (Bug 1342051).
+    this._clearCache();
     AutoRefreshHighlighter.prototype.destroy.call(this);
   },