Bug 1543098 - Emit executionContextDestroyed and executionContextCreated when the page goes into/out of the BF Cache. r=ato

Differential Revision: https://phabricator.services.mozilla.com/D28959

--HG--
extra : moz-landing-system : lando

remote/domains/content/Runtime.jsm

@@ -27,6 +27,12 @@ class Runtime extends ContentProcessDomain {
       this.chromeEventHandler.addEventListener("DOMWindowCreated", this,
         {mozSystemGroup: true});
 
+      // Listen for pageshow and pagehide to track pages going in/out to/from the BF Cache
+      this.chromeEventHandler.addEventListener("pageshow", this,
+        {mozSystemGroup: true});
+      this.chromeEventHandler.addEventListener("pagehide", this,
+        {mozSystemGroup: true});
+
       Services.obs.addObserver(this, "inner-window-destroyed");
 
       // Spin the event loop in order to send the `executionContextCreated` event right
@@ -52,11 +58,15 @@ class Runtime extends ContentProcessDomain {
       this.enabled = false;
       this.chromeEventHandler.removeEventListener("DOMWindowCreated", this,
         {mozSystemGroup: true});
+      this.chromeEventHandler.removeEventListener("pageshow", this,
+        {mozSystemGroup: true});
+      this.chromeEventHandler.removeEventListener("pagehide", this,
+        {mozSystemGroup: true});
       Services.obs.removeObserver(this, "inner-window-destroyed");
     }
   }
 
-  handleEvent({type, target}) {
+  handleEvent({type, target, persisted}) {
     const frameId = target.defaultView.windowUtils.outerWindowID;
     const id = target.defaultView.windowUtils.currentInnerWindowID;
     switch (type) {
@@ -71,6 +81,32 @@ class Runtime extends ContentProcessDomain {
         },
       });
       break;
+
+    case "pageshow":
+      // `persisted` is true when this is about a page being resurected from BF Cache
+      if (!persisted) {
+        return;
+      }
+      this.emit("Runtime.executionContextCreated", {
+        context: {
+          id,
+          auxData: {
+            isDefault: target == this.content.document,
+            frameId,
+          },
+        },
+      });
+      break;
+
+    case "pagehide":
+      // `persisted` is true when this is about a page being frozen into BF Cache
+      if (!persisted) {
+        return;
+      }
+      this.emit("Runtime.executionContextDestroyed", {
+        executionContextId: id,
+      });
+      break;
     }
   }
 

remote/test/browser/browser_runtime_executionContext.js

@@ -59,20 +59,42 @@ async function testCDP() {
   ok(context1.auxData.isDefault, "The execution context is the default one");
   ok(!!context1.auxData.frameId, "The execution context has a frame id set");
 
-  const executionContextCreated = Runtime.executionContextCreated();
+  info("Navigate to a new URL");
+  const executionContextDestroyed2 = Runtime.executionContextDestroyed();
+  const executionContextCreated2 = Runtime.executionContextCreated();
 
   const url = "data:text/html;charset=utf-8,test-page";
   const { frameId } = await Page.navigate({ url });
   ok(true, "A new page has been loaded");
   is(frameId, context1.auxData.frameId, "Page.navigate returns the same frameId than executionContextCreated");
 
-  const { context: context2 } = await executionContextCreated;
+  let { executionContextId } = await executionContextDestroyed2;
+  is(executionContextId, context1.id, "The destroyed event reports the previous context id");
+
+  const { context: context2 } = await executionContextCreated2;
   ok(!!context2.id, "The execution context has an id");
   isnot(context1.id, context2.id, "The new execution context has a different id");
   ok(context2.auxData.isDefault, "The execution context is the default one");
   is(context2.auxData.frameId, frameId, "The execution context frame id is the same " +
-    "the one returned by Page.navigate");
+    "than the one returned by Page.navigate");
 
+  isnot(executionContextId, context2.id, "The destroyed id is different from the " +
+    "created one");
+
+  // Navigates back to the previous page.
+  // This should resurect the original document from the BF Cache and recreate the
+  // context for it
+  info("Navigate back to the previous document");
+  const executionContextDestroyed3 = Runtime.executionContextDestroyed();
+  const executionContextCreated3 = Runtime.executionContextCreated();
+  gBrowser.selectedBrowser.goBack();
+  const { context: context3 } = await executionContextCreated3;
+  is(context3.id, context1.id, "The new execution context should be the same than the first one");
+  ok(context3.auxData.isDefault, "The execution context is the default one");
+  is(context3.auxData.frameId, frameId, "The execution context frame id is always the same");
+
+  ({ executionContextId } = await executionContextDestroyed3);
+  is(executionContextId, context2.id, "The destroyed event reports the previous context id");
   await client.close();
   ok(true, "The client is closed");