Breakpad Linux dumper: Make StabsReader independent of endianness and word size.

StabsReader simply applies a reinterpret_cast to treat the stab entry data
as an array of 'struct nlist' structures, making the parser specific on the
host endianness, word size, and alignment rules. On Mac OS X, a single fat
binary file may contain object files of different ABIs, of which the user
chooses one at run time.

This patch changes the parser to read the data using the google_breakpad::
ByteCursor class, which can handle different endiannesses and word sizes.
The StabsReader constructor now takes arguments indicating the endianness
of the data and the size of each entry's value field. The patch changes
src/common/linux/dump_symbols.cc to pass the new argument.

This patch changes the StabsReader unit tests to use the google_breakpad::
TestAssembler classes to generate test data, rather than reading it from a
file. This makes it easy to generate test data in various endiannesses and
word sizes. It also adds tests for the new parser behaviors.

a=jimblandy, r=thestig


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@583 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/testdata/stabs_reader_unittest.input1

@@ -1,19 +0,0 @@
-SO      10   11   0x02 builddir/
-FUN     20   21   0x12 not the SO with source file name we expected 
-SO      30   31   0x22 
-SO      40   41   0x32 builddir1/
-SO      50   51   0x42 file1.c
-LSYM    60   61   0x52 not the FUN we're looking for
-FUN     70   71   0x62 fun1
-BINCL   80   81   0x72 something to ignore in a FUN body
-SLINE   90   91   0x82
-SOL    100  101   0x92 header.h
-SLINE  110  111  0x102
-FUN    120  121  0x112 fun2:some stabs type info here, to trim from the name
-SLINE  130  131  0x122
-SOL    140  141  0x132 file1.c
-SLINE  150  151  0x142
-SO     160  161  0x152
-LSYM   170  171  0x162
-SO     180  181  0x182 file3.c
-SO     190  191  0x192

src/common/testdata/stabs_reader_unittest.input2

@@ -1 +0,0 @@
-SO      10   11   0x12 file2-1.c

src/common/testdata/stabs_reader_unittest.input3

@@ -1,2 +0,0 @@
-SO      10   11   0x12 file3-1.c
-FUN     20   21   0x22 fun3_1

src/common/testdata/stabs_reader_unittest.input4

@@ -1 +0,0 @@
-SO      10   11   0x12 build-directory/

src/common/testdata/stabs_reader_unittest.input5

@@ -1,2 +0,0 @@
-SO      10   11   0x12 file5-1.c
-SO      20   21   0x22 file5-2.c

src/common/testdata/stabs_reader_unittest.input6

@@ -1,8 +0,0 @@
-cu-boundary antimony
-SO      10   11   0x12 antimony
-FUN     20   21   0x22 arsenic
-SO      30   31   0x32
-cu-boundary aluminum
-SO      40   41   0x42 aluminum
-FUN     50   51   0x52 selenium
-SO      60   61   0x62