Revert of Do not allow asan_symbolize.py to fall back to addr2line/atos....

Revert of Do not allow asan_symbolize.py to fall back to addr2line/atos. (patchset #1 id:1 of https://codereview.chromium.org/983083004/)

Reason for revert:
Turns out the fall back to addr2line happens routinely. We need to fix that before proceeding with this change.

Original issue's description:
> Do not allow asan_symbolize.py to fall back to addr2line/atos.
>
> For performance reasons we want to stick to llvm-symbolizer.
> This also rolls the third-party asan_symbolize.py to r231492.
>
> BUG=415179
> TBR=glider@chromium.org
> NOTRY=true
>
> Committed: https://crrev.com/2ee9a8ae1e39433fc8df07c27256963715747bbb
> Cr-Commit-Position: refs/heads/master@{#319460}

TBR=glider@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=415179

Review URL: https://codereview.chromium.org/1017793002

Cr-Commit-Position: refs/heads/master@{#320955}

tools/valgrind/asan/asan_symbolize.py

@@ -246,9 +246,6 @@ def main():
 
   disable_buffering()
   set_symbolizer_path()
-  # Disallow fallback to addr2line/atos if llvm-symbolizer is not present. Those
-  # are slow and we don't want to use them ever.
-  asan_symbolize.allow_system_symbolizer = False
   asan_symbolize.demangle = True
   asan_symbolize.fix_filename_patterns = args.strip_path_prefix
   # Most source paths for Chromium binaries start with

tools/valgrind/asan/third_party/README.chromium

 Name: asan_symbolize.py
 License: University of Illinois Open Source License.
-Version: r231492
+Version: r227327
 URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/asan/scripts/asan_symbolize.py?view=co&content-type=text%2Fplain
 Security Critical: no
 

tools/valgrind/asan/third_party/asan_symbolize.py

@@ -23,7 +23,6 @@ sysroot_path = None
 binary_name_filter = None
 fix_filename_patterns = None
 logfile = sys.stdin
-allow_system_symbolizer = True
 
 # FIXME: merge the code that calls fix_filename().
 def fix_filename(file_name):
@@ -393,8 +392,6 @@ class SymbolizationLoop(object):
           [BreakpadSymbolizerFactory(binary), self.llvm_symbolizers[binary]])
     result = symbolizers[binary].symbolize(addr, binary, offset)
     if result is None:
-      if not allow_system_symbolizer:
-        raise Exception('Failed to launch or use llvm-symbolizer.')
       # Initialize system symbolizer only if other symbolizers failed.
       symbolizers[binary].append_symbolizer(
           SystemSymbolizerFactory(self.system, addr, binary))