Reapply "IDB: direct reads for blobs"

This relands commit 60632268eadd3051d4ec88d62292b160682f8a56.

Difference to original: added support for AsDataPipeGetter and
extended blob-contenttype.any.js WPT to cover this case.

Original change's description:
> IDB: direct reads for blobs
>
> For the standard case of a page reading IDB data from the blob store,
> don't go through the blob registry on the i/o thread and instead
> connect the IDB bucket thread directly to the renderer.
>
> In some other (rarer) cases the blob registry is still used. This
> is accomplished by *additionally* registering a blob with
> BlobStorageContext using the same UUID, which is necessary for:
>
> * WriteBlobToFile(), which does lookup by UUID
> * loading data for a blob:// URL, i.e. mojom::Blob::Load, which is
>   thunked through to the registry blob because implementation is non-
>   trivial
>
> Bug: 373684390
> Change-Id: I9235f23303e4e6a05bf12a8acff32a5fb4e2a565
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6113789
> Commit-Queue: Evan Stade <[email protected]>
> Reviewed-by: Steve Becker <[email protected]>
> Cr-Commit-Position: refs/heads/main@{#1400627}

Bug: 373684390
Change-Id: Ie555cf4b583b862d306c43e3e4be76e957ea6c5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6138579
Reviewed-by: Steve Becker <[email protected]>
Commit-Queue: Evan Stade <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1401872}

IndexedDB/blob-contenttype.any.js

@@ -16,23 +16,39 @@ indexeddb_test(
         tx.objectStore('store').put(blob, 'key');
 
         tx.oncomplete = t.step_func(function() {
-            var tx = db.transaction('store', 'readonly', {durability: 'relaxed'});
-            tx.objectStore('store').get('key').onsuccess = t.step_func(function(e) {
+          var tx = db.transaction('store', 'readonly', {durability: 'relaxed'});
+          tx.objectStore('store').get('key').onsuccess =
+              t.step_func(function(e) {
                 var result = e.target.result;
                 assert_equals(result.type, type, 'Blob type should survive round-trip');
 
+                // Test createObjectURL i.e. a blob:// URL.
                 var url = URL.createObjectURL(result);
                 var xhr = new XMLHttpRequest(), async = true;
                 xhr.open('GET', url, async);
                 xhr.send();
                 xhr.onreadystatechange = t.step_func(function() {
-                    if (xhr.readyState !== XMLHttpRequest.DONE)
-                        return;
-                    assert_equals(xhr.getResponseHeader('Content-Type'), type,
-                                  'Blob type should be preserved when fetched');
+                  if (xhr.readyState !== XMLHttpRequest.DONE)
+                    return;
+                  assert_equals(
+                      xhr.getResponseHeader('Content-Type'), type,
+                      'Blob type should be preserved when fetched');
+
+                  // Test POSTing blob in request.
+                  var xhr2 = new XMLHttpRequest();
+                  xhr2.open('POST', '../xhr/resources/content.py', true);
+                  xhr2.send(result);
+
+                  xhr2.onreadystatechange = t.step_func(function() {
+                    if (xhr2.readyState !== XMLHttpRequest.DONE)
+                      return;
+                    assert_equals(xhr2.status, 200);
+                    assert_equals(xhr2.getResponseHeader('X-Request-Content-Type'), type);
+                    assert_equals(xhr2.response, 'mulderscully');
                     t.done();
+                  });
                 });
-            });
+              });
         });
     },
     'Ensure that content type round trips when reading blob data'