Add a string pool to store functions names

- Added StringView which is used as a reference to a string, but
doesn't own the string.
- Removed the old string pool in DwarfCUToModule::FilePrivate, since
it's doing string copy.
- Added a string pool in Module to store functions/inline origins'
names (mangled and demangled).
- The peak memory usage drops from 20.6 GB to 12.5 GB when disabling
inline records and drops from 36 GB to 20.3 GB when enabling inline records.

Bug: chromium:1246974, chromium:1250351
Change-Id: Ie7e9740ea10c1930a0fc58c6becaae2d718b83b8
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3189410
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

src/common/string_view.h

@@ -0,0 +1,113 @@
+// Copyright (c) 2021 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef COMMON_STRING_VIEW_H__
+#define COMMON_STRING_VIEW_H__
+
+#include <cassert>
+#include <cstring>
+#include <ostream>
+#include "common/using_std_string.h"
+
+namespace google_breakpad {
+
+// A StringView is a string reference to a string object, but not own the
+// string object.
+class StringView {
+ private:
+  // The start of the string, in an external buffer. It doesn't have to be
+  // null-terminated.
+  const char* data_ = "";
+
+  size_t length_ = 0;
+
+ public:
+  // Construct an empty StringView.
+  StringView() = default;
+
+  // Disallow construct StringView from nullptr.
+  StringView(nullptr_t) = delete;
+
+  // Construct a StringView from a cstring.
+  StringView(const char* str) : data_(str) {
+    assert(str);
+    length_ = strlen(str);
+  }
+
+  // Construct a StringView from a cstring with fixed length.
+  StringView(const char* str, size_t length) : data_(str), length_(length) {
+    assert(str);
+  }
+
+  // Construct a StringView from an std::string.
+  StringView(const string& str) : data_(str.data()), length_(str.length()) {}
+
+  string str() const { return string(data_, length_); }
+
+  const char* data() const { return data_; }
+
+  bool empty() const { return length_ == 0; }
+
+  size_t size() const { return length_; }
+
+  int compare(StringView rhs) const {
+    size_t min_len = std::min(size(), rhs.size());
+    int res = memcmp(data_, rhs.data(), min_len);
+    if (res != 0)
+      return res;
+    if (size() == rhs.size())
+      return 0;
+    return size() < rhs.size() ? -1 : 1;
+  }
+};
+
+inline bool operator==(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) == 0;
+}
+
+inline bool operator!=(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) != 0;
+}
+
+inline bool operator<(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) < 0;
+}
+
+inline bool operator>(StringView lhs, StringView rhs) {
+  return lhs.compare(rhs) > 0;
+}
+
+inline std::ostream& operator<<(std::ostream& os, StringView s) {
+  os << s.str();
+  return os;
+}
+
+}  // namespace google_breakpad
+
+#endif  // COMMON_STRING_VIEW_H__