Replace MMappedRange with MinidumpMemoryRange.

Replace MMappedRange with MinidumpMemoryRange.

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

The MemoryRange class was added in r895 (http://breakpad.appspot.com/332001),
which is largely based on MMappedRange but generalized to be used in other
code. However, MemoryRange does not support minidump data structures. This
patch adds a MinidumpMemoryRange class that extends MemoryRange to handle
minidump data structures, which can then replace MMappedRange.

As with MemoryRange, MinidumpMemoryRange is unit tested.

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.

[Ben Chan]

http://breakpad.appspot.com/335001/diff/1/5
File src/tools/linux/md2core/minidump-2-core.cc (right):

http://breakpad.appspot.com/335001/diff/1/5#newcode388
Line 388: if
(!strstr(full_file.GetAsciiMDString(sysinfo->csd_version_rva).c_str(),
I renamed GetString to GetAsciiMDString to emphasize that this method assumes a
ASCII-only string, and doesn't do any UTF-16/UTF-8 conversion.

[Ben Chan]

Rebased to ToT.

[Michael Krebs]

LGTM