Refactor code in preparation of merging with the fork in Chromium OS.

This patch is part of a bigger patch that helps merging the breakpad code
with the modified version in Chromium OS.

Specifically, this patch makes the following changes:
1. Add a MemoryRange class for encapsulating and checking read access
   to a contiguous range of memory.
2. Add a MemoryMappedFile class for mapping a file into memory for
   read-only access.
3. Refactor other source code to use MemoryMappedFile.

BUG=455
TEST=Tested the following:
1. Build on 32-bit and 64-bit Linux with gcc 4.4.3 and gcc 4.6.
2. Build on Mac OS X 10.6.8 with gcc 4.2 and clang 3.0 (with latest gmock).
3. All unit tests pass.
4. Run minidump-2-core to covnert a minidump file to a core file.
Review URL: http://breakpad.appspot.com/332001

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@895 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/linux/memory_mapped_file.h

@@ -0,0 +1,86 @@
+// Copyright (c) 2011, 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.
+
+// memory_mapped_file.h: Define the google_breakpad::MemoryMappedFile
+// class, which maps a file into memory for read-only access.
+
+#ifndef COMMON_LINUX_MEMORY_MAPPED_FILE_H_
+#define COMMON_LINUX_MEMORY_MAPPED_FILE_H_
+
+#include "common/basictypes.h"
+#include "common/memory_range.h"
+
+namespace google_breakpad {
+
+// A utility class for mapping a file into memory for read-only access of
+// the file content. Its implementation avoids calling into libc functions
+// by directly making system calls for open, close, mmap, and munmap.
+class MemoryMappedFile {
+ public:
+  MemoryMappedFile();
+
+  // Constructor that calls Map() to map a file at |path| into memory.
+  // If Map() fails, the object behaves as if it is default constructed.
+  explicit MemoryMappedFile(const char* path);
+
+  ~MemoryMappedFile();
+
+  // Maps a file at |path| into memory, which can then be accessed via
+  // content() as a MemoryRange object or via data(), and returns true on
+  // success. Mapping an empty file will succeed but with data() and size()
+  // returning NULL and 0, respectively. An existing mapping is unmapped
+  // before a new mapping is created.
+  bool Map(const char* path);
+
+  // Unmaps the memory for the mapped file. It's a no-op if no file is
+  // mapped.
+  void Unmap();
+
+  // Returns a MemoryRange object that covers the memory for the mapped
+  // file. The MemoryRange object is empty if no file is mapped.
+  const MemoryRange& content() const { return content_; }
+
+  // Returns a pointer to the beginning of the memory for the mapped file.
+  // or NULL if no file is mapped or the mapped file is empty.
+  const void* data() const { return content_.data(); }
+
+  // Returns the size in bytes of the mapped file, or zero if no file
+  // is mapped.
+  size_t size() const { return content_.length(); }
+
+ private:
+  // Mapped file content as a MemoryRange object.
+  MemoryRange content_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
+};
+
+}  // namespace google_breakpad
+
+#endif  // COMMON_LINUX_MEMORY_MAPPED_FILE_H_