Allow empty read in FetchDataLoaderAsDataPipe

ByteConsumer::BeginRead() may return Result::kOK with no available
read data. FetchDataLoaderAsDataPipe should handle zero read as other
ByteConsumer::Client do.

Bug: 807954
Change-Id: I47186ccc01d10c8ff18bdf749376598ee75342a7
Reviewed-on: https://chromium-review.googlesource.com/1096515Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567503}

third_party/WebKit/LayoutTests/TestExpectations

@@ -1756,7 +1756,6 @@ crbug.com/691944 virtual/outofblink-cors/external/wpt/service-workers/service-wo
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/fetch-cors-xhr.https.html [ Failure Crash ]
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/fetch-event.https.html [ Failure Crash ]
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/fetch-event-network-error.https.html [ Crash ]
-crbug.com/807954 virtual/outofblink-cors/external/wpt/service-workers/service-worker/fetch-event-respond-with-readable-stream-chunk.https.html [ Crash ]
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/fetch-request-fallback.https.html [ Crash Failure ]
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/performance-timeline.https.html [ Crash ]
 crbug.com/736308 virtual/outofblink-cors/external/wpt/service-workers/service-worker/redirected-response.https.html [ Crash ]
@@ -3635,8 +3634,6 @@ crbug.com/626703 external/wpt/workers/opaque-origin.html [ Failure Crash Timeout
 crbug.com/626703 external/wpt/html/rendering/non-replaced-elements/margin-collapsing-quirks/multicol-quirks-mode.html [ Pass Crash ]
 crbug.com/626703 external/wpt/html/rendering/non-replaced-elements/margin-collapsing-quirks/multicol-standards-mode.html [ Pass Crash Failure ]
 crbug.com/762017 external/wpt/html/semantics/embedded-content/media-elements/video_loop_base.html [ Pass Crash ]
-crbug.com/807954 external/wpt/service-workers/service-worker/fetch-event-respond-with-readable-stream-chunk.https.html [ Crash ]
-crbug.com/807954 virtual/service-worker-servicification/external/wpt/service-workers/service-worker/fetch-event-respond-with-readable-stream-chunk.https.html [ Crash ]
 
 # Other untriaged test failures, timeouts and crashes from newly-imported WPT tests.
 crbug.com/666703 external/wpt/html/browsers/sandboxing/sandbox-disallow-same-origin.html [ Timeout ]

third_party/blink/renderer/core/fetch/fetch_data_loader.cc

@@ -519,21 +519,24 @@ class FetchDataLoaderAsDataPipe final : public FetchDataLoader,
       if (result == BytesConsumer::Result::kShouldWait)
         return;
       if (result == BytesConsumer::Result::kOk) {
-        DCHECK_GT(available, 0UL);
-        uint32_t num_bytes = available;
-        MojoResult mojo_result = out_data_pipe_->WriteData(
-            buffer, &num_bytes, MOJO_WRITE_DATA_FLAG_NONE);
-        if (mojo_result == MOJO_RESULT_OK) {
-          result = consumer_->EndRead(num_bytes);
-        } else if (mojo_result == MOJO_RESULT_SHOULD_WAIT) {
+        if (available == 0) {
           result = consumer_->EndRead(0);
-          should_wait = true;
-          data_pipe_watcher_.ArmOrNotify();
         } else {
-          result = consumer_->EndRead(0);
-          StopInternal();
-          client_->DidFetchDataLoadFailed();
-          return;
+          uint32_t num_bytes = available;
+          MojoResult mojo_result = out_data_pipe_->WriteData(
+              buffer, &num_bytes, MOJO_WRITE_DATA_FLAG_NONE);
+          if (mojo_result == MOJO_RESULT_OK) {
+            result = consumer_->EndRead(num_bytes);
+          } else if (mojo_result == MOJO_RESULT_SHOULD_WAIT) {
+            result = consumer_->EndRead(0);
+            should_wait = true;
+            data_pipe_watcher_.ArmOrNotify();
+          } else {
+            result = consumer_->EndRead(0);
+            StopInternal();
+            client_->DidFetchDataLoadFailed();
+            return;
+          }
         }
       }
       switch (result) {