Reland "Bounce Blob URL revoking through the UI thread to give navigation a chance."

This is a reland of a3dd29b2.

Original change's description:
> Bounce Blob URL revoking through the UI thread to give navigation a chance.
>
> Navigation IPCs are handled on the UI thread so if a blob URL is revoked
> immediately after navigating the revocation will almost always happen before
> the navigation code has had a chance to post a task back to the IO thread to
> actually perform the request. With this change revocation is hopefully
> delayed just long enough to make navigation work again.
>
> Bug: 807639
> Change-Id: I2afde86dd203c61cbb03cc02ac62ec21c7e7d704
> Reviewed-on: https://chromium-review.googlesource.com/899666
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#534119}

TBR=mek@chromium.org,jochen@chromium.org

Bug: 807639,808759
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I5033422d57ac7672e761045f7871c6aed29368b9
Reviewed-on: https://chromium-review.googlesource.com/900191
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534257}

content/browser/blob_storage/blob_dispatcher_host.cc

@@ -89,6 +89,25 @@ void BlobDispatcherHost::OnRegisterPublicBlobURL(const GURL& public_url,
   public_blob_urls_.insert(public_url);
 }
 
+namespace {
+
+void RevokePublicBlobURLHelperIO(
+    scoped_refptr<ChromeBlobStorageContext> context,
+    const GURL& public_url) {
+  context->context()->RevokePublicBlobURL(public_url);
+}
+
+void RevokePublicBlobURLHelperUI(
+    scoped_refptr<ChromeBlobStorageContext> context,
+    const GURL& public_url) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+                          base::BindOnce(&RevokePublicBlobURLHelperIO,
+                                         std::move(context), public_url));
+}
+
+}  // namespace
+
 void BlobDispatcherHost::OnRevokePublicBlobURL(const GURL& public_url) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   if (!public_url.is_valid()) {
@@ -103,8 +122,10 @@ void BlobDispatcherHost::OnRevokePublicBlobURL(const GURL& public_url) {
                               BDH_TRACING_ENUM_LAST);
     return;
   }
-  context()->RevokePublicBlobURL(public_url);
   public_blob_urls_.erase(public_url);
+  BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+                          base::BindOnce(&RevokePublicBlobURLHelperUI,
+                                         blob_storage_context_, public_url));
 }
 
 storage::BlobStorageContext* BlobDispatcherHost::context() {

content/test/data/download/download-attribute-blob.html

@@ -15,6 +15,7 @@ var blob = new Blob(['hello world!'], {type: 'text/plain'});
 var url = URL.createObjectURL(blob);
 anchorElement.href = url;
 anchorElement.click();
+URL.revokeObjectURL(url);
 </script>
 </body>
 </html>

testing/buildbot/filters/mojo.fyi.network_content_browsertests.filter

@@ -126,4 +126,7 @@
 -CrossSiteDocumentBlockingTest.RangeRequest
 
 # Flakes https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.linux%2FLinux_Tests__dbg__1_%2F69105%2F%2B%2Frecipes%2Fsteps%2Fnetwork_service_content_browsertests%2F0%2Flogs%2FWebContentsImplBrowserTest.DownloadImage_Allow_FileImage%2F0
--WebContentsImplBrowserTest.DownloadImage_Allow_FileImage
+-WebContentsImplBrowserTest.DownloadImage_Allow_FileImage
+
+# https://crbug.com/808759
+-DownloadContentTest.DownloadAttributeBlobURL