Blimp: improve FontFetcher mojo ipc unittest

FontFetcherMojoImplUnittest used to just create the impl object directly
and fire methods at it. In this change, we use the mojo services
framework for service binding and communication.

BUG=

Review-Url: https://codereview.chromium.org/2534033002
Cr-Commit-Position: refs/heads/master@{#434817}

blimp/engine/mojo/font_fetcher_mojo_impl_unittest.cc

@@ -55,18 +55,20 @@ class FontFetcherMojoImplUnittest : public testing::Test {
       : font_fetcher_mojo_impl_(new FakeFontDataFetcher()) {}
   ~FontFetcherMojoImplUnittest() override {}
 
+ protected:
+  base::MessageLoop message_loop_;
   FontFetcherMojoImpl font_fetcher_mojo_impl_;
 };
 
-// TODO(mlliu): add tests later to do a full IPC test, calling the FontFetcher
-// API via the corresponding Mojo client interface.
 TEST_F(FontFetcherMojoImplUnittest, VerifyWriteToDataPipe) {
+  mojom::FontFetcherPtr mojo_ptr;
+  font_fetcher_mojo_impl_.BindRequest(GetProxy(&mojo_ptr));
+
   // Expect that dummy font data is written correctly to a Mojo DataPipe.
-  font_fetcher_mojo_impl_.GetFontStream(kFakeHash,
-                                        base::Bind(&VerifyDataWriteCorrectly));
+  mojo_ptr->GetFontStream(kFakeHash, base::Bind(&VerifyDataWriteCorrectly));
 
   // Expect empty handle if the font stream is empty.
-  font_fetcher_mojo_impl_.GetFontStream("", base::Bind(&VerifyEmptyDataWrite));
+  mojo_ptr->GetFontStream("", base::Bind(&VerifyEmptyDataWrite));
 }
 
 }  // namespace