[ MimeHandlerView ] DidLoad should affect frame container once

MimeHandlerViewContainerManager::DidLoad is used to notify the renderer that
PostMessageSupport can be active and forward messages. The current logic
activates the first PostMessageSupport with a matching URL. This should be the
first PostMessageSupport that is *not* active and has a matching URL.

TBR=wjmaclean@chromium.org

Bug: 957373
Change-Id: Ic2925b593081ec5ac83d6950a1f57243d2b41e45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1608820Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659036}

extensions/browser/guest_view/mime_handler_view/mime_handler_view_browsertest.cc

@@ -22,6 +22,7 @@
 #include "components/app_modal/native_app_modal_dialog.h"
 #include "components/guest_view/browser/test_guest_view_manager.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/content_features.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/test/browser_test_utils.h"
@@ -574,3 +575,41 @@ IN_PROC_BROWSER_TEST_F(MimeHandlerViewBrowserPluginSpecificTest,
   }
   EXPECT_EQ(GetMouseCaptureWidget(embedder_web_contents), guest_widget);
 }
+
+// Helper class to wait for document load event in the main frame.
+class DocumentLoadComplete : public content::WebContentsObserver {
+ public:
+  explicit DocumentLoadComplete(content::WebContents* web_contents)
+      : content::WebContentsObserver(web_contents) {}
+  ~DocumentLoadComplete() override {}
+
+  void DocumentOnLoadCompletedInMainFrame() override {
+    did_load_ = true;
+    run_loop_.Quit();
+  }
+
+  void Wait() {
+    if (!did_load_)
+      run_loop_.Run();
+  }
+
+ private:
+  bool did_load_ = false;
+  base::RunLoop run_loop_;
+};
+
+IN_PROC_BROWSER_TEST_P(MimeHandlerViewCrossProcessTest,
+                       ActivatePostMessageSupportOnce) {
+  RunTest("test_embedded.html");
+  // Attach a second <embed>.
+  ASSERT_TRUE(content::ExecJs(GetEmbedderWebContents(),
+                              "const e = document.createElement('embed');"
+                              "e.src = './testEmbedded.csv'; e.type='text/csv';"
+                              "document.body.appendChild(e);"));
+  DocumentLoadComplete(GetGuestViewManager()->WaitForNextGuestCreated()).Wait();
+  // After load, an IPC has been sent to the renderer to update routing IDs for
+  // the guest frame and the content frame (and activate the
+  // PostMessageSupport). Run some JS to Ensure no DCHECKs have fired in the
+  // embedder process.
+  ASSERT_TRUE(content::ExecJs(GetEmbedderWebContents(), "foo = 0;"));
+}
\ No newline at end of file

extensions/renderer/guest_view/mime_handler_view/mime_handler_view_container_manager.cc

@@ -154,6 +154,8 @@ void MimeHandlerViewContainerManager::DidLoad(int32_t element_instance_id,
     return;
   }
   for (auto& frame_container : frame_containers_) {
+    if (frame_container->post_message_support()->is_active())
+      continue;
     if (frame_container->resource_url() != resource_url)
       continue;
     // To ensure the postMessages will be sent to the right target frame, we