Fix an flaky test for parallel download

This CL fixes an issue in DownloadFileWithError that
when injecting an error on a write offset, we should check if
the offset is overwritten by a write operation, rather than just
the beginning offset.
And then we use this fix to fix the flaky MiddleSliceDelayedError
as the same offset will be overwritten twice by 2 streams.

BUG=1105429, 1106059

Change-Id: Iff9b9d796ed5d86c68b24667096e2089564c4c0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401312Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805605}

content/browser/download/download_browsertest.cc

@@ -4311,23 +4311,14 @@ IN_PROC_BROWSER_TEST_F(ParallelDownloadTest,
                                   parameters);
 }
 
-#if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_CHROMEOS) || \
-    defined(OS_ANDROID)
-// Flaky https://crbug.com/1105429, https://crbug.com/1106059.
-// Windows probably use a large receiving buffer size and cause the first slice
-// to start at a offset > 0.
-#define MAYBE_MiddleSliceDelayedError DISABLED_MiddleSliceDelayedError
-#else
-#define MAYBE_MiddleSliceDelayedError MiddleSliceDelayedError
-#endif
 // Verify that if the second request fails after the beginning request takes
 // over and completes its slice, download should complete.
-IN_PROC_BROWSER_TEST_F(ParallelDownloadTest, MAYBE_MiddleSliceDelayedError) {
+IN_PROC_BROWSER_TEST_F(ParallelDownloadTest, MiddleSliceDelayedError) {
   scoped_refptr<TestFileErrorInjector> injector(
       TestFileErrorInjector::Create(DownloadManagerForShell(shell())));
 
   TestFileErrorInjector::FileErrorInfo err = {
-      TestFileErrorInjector::FILE_OPERATION_WRITE, 0,
+      TestFileErrorInjector::FILE_OPERATION_WRITE, 1,
       download::DOWNLOAD_INTERRUPT_REASON_FILE_NO_SPACE};
   err.data_write_offset = 1699050;
   injector->InjectError(err);

content/public/test/test_file_error_injector.cc

@@ -186,7 +186,9 @@ DownloadFileWithError::ValidateAndWriteDataToFile(int64_t offset,
       download::DownloadFileImpl::ValidateAndWriteDataToFile(
           offset, data, bytes_to_validate, bytes_to_write);
   if (error_info_.data_write_offset == -1 ||
-      offset == error_info_.data_write_offset) {
+      ((offset <= error_info_.data_write_offset) &&
+       (offset + bytes_to_write >=
+        static_cast<size_t>(error_info_.data_write_offset)))) {
     return ShouldReturnError(TestFileErrorInjector::FILE_OPERATION_WRITE,
                              origin_error);
   }

content/public/test/test_file_error_injector.h

@@ -67,7 +67,7 @@ class TestFileErrorInjector
     download::DownloadInterruptReason error;  // Error to inject.
     int64_t stream_offset = -1;     // Offset of the error stream.
     int64_t stream_bytes_written = -1;  // Bytes written to the error stream.
-    // If > 0, only write calls to this offset will generate errors.
+    // If > 0, only write operations covering this offset will generate errors.
     // Otherwise, all file writes will generate errors.
     int64_t data_write_offset = -1;
   };