Revert "Remove 'using' directives in web_idb_cursor_impl_unittest.cc"

This reverts commit 5ac9ece1.

Reason for revert:
Reverting the "move content/renderer/indexed_db/ to Blink" CL.  This
commit touches a file that was created by that CL, so reverting it.
See these bugs for more info:
https://crbug.com/899446
https://crbug.com/717812

Original change's description:
> Remove 'using' directives in web_idb_cursor_impl_unittest.cc
> 
> All of the 'blink::*' directives should be unnecessary (now that the code
> is within Blink.) Remove the testing::StrictMock 'using' too, and just
> "expand" it at its single usage point.
> 
> Change-Id: I3171d05f41364fa134c2ee781e93178d831d4eab
> Reviewed-on: https://chromium-review.googlesource.com/c/1301458
> Commit-Queue: Victor Costan <pwnall@chromium.org>
> Reviewed-by: Victor Costan <pwnall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#603049}

TBR=fs@opera.com,pwnall@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I10c3fe89cdb7708d8e66978474f6a0299b775af7
Reviewed-on: https://chromium-review.googlesource.com/c/1305395
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Chase Phillips <cmp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603590}

third_party/blink/renderer/modules/indexeddb/web_idb_cursor_impl_unittest.cc

@@ -20,6 +20,17 @@
 #include "third_party/blink/renderer/platform/testing/testing_platform_support.h"
 #include "third_party/blink/renderer/platform/testing/unit_test_helpers.h"
 
+using blink::IndexedDBKey;
+using blink::WebBlobInfo;
+using blink::WebData;
+using blink::WebIDBCallbacks;
+using blink::WebIDBKey;
+using blink::kWebIDBKeyTypeNumber;
+using blink::WebIDBValue;
+using blink::WebString;
+using blink::WebVector;
+using testing::StrictMock;
+
 namespace blink {
 
 namespace {
@@ -79,7 +90,7 @@ class MockCursorImpl : public mojom::blink::IDBCursor {
   mojo::AssociatedBinding<IDBCursor> binding_;
 };
 
-class MockContinueCallbacks : public testing::StrictMock<MockWebIDBCallbacks> {
+class MockContinueCallbacks : public StrictMock<MockWebIDBCallbacks> {
  public:
   MockContinueCallbacks(IndexedDBKey* key = nullptr,
                         WebVector<WebBlobInfo>* blobs = nullptr)