Add truncation to StreamCopyOrMoveImpl and test case.

BUG=410126
TEST=content_unittests

Review URL: https://codereview.chromium.org/536453007

Cr-Commit-Position: refs/heads/master@{#293082}

content/browser/fileapi/file_system_operation_impl_unittest.cc

@@ -50,6 +50,15 @@ void AssertFileErrorEq(const tracked_objects::Location& from_here,
   ASSERT_EQ(expected, actual) << from_here.ToString();
 }
 
+void AssertFileErrorEqWithClosure(
+    const tracked_objects::Location& from_here,
+    base::File::Error expected,
+    base::Closure closure,
+    base::File::Error actual) {
+  ASSERT_EQ(expected, actual) << from_here.ToString();
+  closure.Run();
+}
+
 }  // namespace
 
 // Test class for FileSystemOperationImpl.
@@ -1287,4 +1296,34 @@ TEST_F(FileSystemOperationImplTest,
   EXPECT_EQ(expected_usage, usage);
 }
 
+TEST_F(FileSystemOperationImplTest,
+       TestCopySuccessSrcFileWithDifferentFileSize) {
+  FileSystemURL src_file(CreateFile("src"));
+  FileSystemURL dest_file(CreateFile("dest"));
+
+  {
+    base::RunLoop run_loop;
+    operation_runner()->Truncate(
+        dest_file, 6,
+        base::Bind(&AssertFileErrorEqWithClosure,
+           FROM_HERE,
+           base::File::FILE_OK,
+           run_loop.QuitClosure()));
+    run_loop.Run();
+  }
+
+  {
+    base::RunLoop run_loop;
+    operation_runner()->Copy(
+        src_file, dest_file, FileSystemOperation::OPTION_NONE,
+        FileSystemOperationRunner::CopyProgressCallback(),
+        base::Bind(&AssertFileErrorEqWithClosure,
+                   FROM_HERE,
+                   base::File::FILE_OK,
+                   run_loop.QuitClosure()));
+    run_loop.Run();
+  }
+  EXPECT_EQ(0, GetFileSize("dest"));
+}
+
 }  // namespace content

webkit/browser/fileapi/copy_or_move_operation_delegate.cc

@@ -423,10 +423,12 @@ class StreamCopyOrMoveImpl
 
     // To use FileStreamWriter, we need to ensure the destination file exists.
     operation_runner_->CreateFile(
-        dest_url_, false /* exclusive */,
+        dest_url_,
+        true /* exclusive */,
         base::Bind(&StreamCopyOrMoveImpl::RunAfterCreateFileForDestination,
                    weak_factory_.GetWeakPtr(),
-                   callback, file_info.last_modified));
+                   callback,
+                   file_info.last_modified));
   }
 
   void RunAfterCreateFileForDestination(
@@ -436,6 +438,33 @@ class StreamCopyOrMoveImpl
     if (cancel_requested_)
       error = base::File::FILE_ERROR_ABORT;
 
+    if (error != base::File::FILE_OK &&
+        error != base::File::FILE_ERROR_EXISTS) {
+      callback.Run(error);
+      return;
+    }
+
+    if (error == base::File::FILE_ERROR_EXISTS) {
+      operation_runner_->Truncate(
+          dest_url_,
+          0 /* length */,
+          base::Bind(&StreamCopyOrMoveImpl::RunAfterTruncateForDestination,
+                     weak_factory_.GetWeakPtr(),
+                     callback,
+                     last_modified));
+      return;
+    }
+    RunAfterTruncateForDestination(
+        callback, last_modified, base::File::FILE_OK);
+  }
+
+  void RunAfterTruncateForDestination(
+      const CopyOrMoveOperationDelegate::StatusCallback& callback,
+      const base::Time& last_modified,
+      base::File::Error error) {
+    if (cancel_requested_)
+      error = base::File::FILE_ERROR_ABORT;
+
     if (error != base::File::FILE_OK) {
       callback.Run(error);
       return;