tracing v2: refactor fake_scattered_buffer class for tests

components/tracing/test/fake_scattered_buffer.cc

Index: components/tracing/test/fake_scattered_buffer.cc
diff --git a/components/tracing/test/fake_scattered_buffer.cc b/components/tracing/test/fake_scattered_buffer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..69d56101f80480684ef82b1ad20be2e24a5e6dfe
--- /dev/null
+++ b/components/tracing/test/fake_scattered_buffer.cc
@@ -0,0 +1,43 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/tracing/test/fake_scattered_buffer.h"
+
+#include <string.h>
+
+#include "base/strings/string_number_conversions.h"
+
+namespace tracing {
+namespace v2 {
+
+FakeScatteredBuffer::FakeScatteredBuffer(size_t chunk_size)
+    : chunk_size_(chunk_size) {}
+
+FakeScatteredBuffer::~FakeScatteredBuffer() {}
+
+ContiguousMemoryRange FakeScatteredBuffer::GetNewBuffer() {
+  std::unique_ptr<uint8_t[]> chunk(new uint8_t[chunk_size_]);
+  uint8_t* begin = chunk.get();
+  memset(begin, 0, chunk_size_);
+  chunks_.push_back(std::move(chunk));
+  return {begin, begin + chunk_size_};
+}
+
+std::string FakeScatteredBuffer::GetChunkAsString(int chunk_index) {
+  return base::HexEncode(chunks_[chunk_index].get(), chunk_size_);
+}
+
+std::string FakeScatteredBuffer::GetBytesAsString(size_t start, size_t length) {
+  std::string hexstr;
+  for (size_t pos = start; pos < start + length; ++pos) {
+    const size_t chunk_idx = pos / chunk_size_;
+    const size_t chunk_off = pos % chunk_size_;
+    DCHECK_LT(chunk_idx, chunks_.size());

[petrcermak, 2016/07/12 10:29:44]

Given that this will only be used in tests, wouldn't it make sense to use a
check that will run even when DCHECK is disabled?

[Primiano Tucci (use gerrit), 2016/07/12 11:04:26]

all bots these days run with DCHECK_ALWAYS_ON (so dchecks are enabled even for
release).
But your comment made me realize that this is not really a dcheck. If we hit
this path this is not a problem with the fake buffer itself, it's the text
fixture doing something wrong, and this should be an expectation failure. (I
can't use assert, they are valid only in TEST_F functions)

+    hexstr += base::HexEncode(&chunks_[chunk_idx].get()[chunk_off], 1);
+  }
+  return hexstr;
+}
+
+}  // namespace v2
+}  // namespace tracing