Reland of Don't IAT patch SetUnhandledExceptionFilter when ASan is ac…

…tive (patchset chromium#1 id:1 of https://codereview.chromium.org/2225453002/ )

Reason for revert:
This patch didn't impact Crashpad.

Original issue's description:
> Revert of Don't IAT patch SetUnhandledExceptionFilter when ASan is active (patchset chromium#1 id:1 of https://codereview.chromium.org/2220583002/ )
>
> Reason for revert:
> This causes crashpad to emit "haven't called UseHandler()" errors later.
>
> Original issue's description:
> > Don't IAT patch SetUnhandledExceptionFilter when ASan is active
> >
> > ASan installs its own exception filter that ClusterFuzz needs to see.
> >
> > R=robertshield@chromium.org,inferno@chromium.org
> > BUG=626373
> >
> > Committed: https://crrev.com/3894e46c8c2702e12d2ddec12f186d7c1cf5c412
> > Cr-Commit-Position: refs/heads/master@{#410077}
>
> TBR=inferno@chromium.org,robertshield@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=626373
>
> Committed: https://crrev.com/07928da2532a9a7d1149d0878d0931dd209f0d3c
> Cr-Commit-Position: refs/heads/master@{#410106}

TBR=robertshield@chromium.org,scottmg@chromium.org,rsesek@chromium.org,aarya@google.com,rnk@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=626373

Review-Url: https://codereview.chromium.org/2217833004
Cr-Commit-Position: refs/heads/master@{#410232}

chrome_elf/chrome_elf_main.cc

@@ -50,6 +50,7 @@ void InitializeCrashReportingForProcess() {
   ChromeCrashReporterClient::InitializeCrashReportingForProcess();
 }
 
+#if !defined(ADDRESS_SANITIZER)
 // chrome_elf loads early in the process and initializes Crashpad. That in turn
 // uses the SetUnhandledExceptionFilter API to set a top level exception
 // handler for the process. When the process eventually initializes, CRT sets
@@ -80,6 +81,7 @@ void DisableSetUnhandledExceptionFilter() {
       SetUnhandledExceptionFilterPatch);
   CHECK(patched == 0);
 }
+#endif // !defined(ADDRESS_SANITIZER)
 
 }  // namespace
 
@@ -112,8 +114,11 @@ BOOL APIENTRY DllMain(HMODULE module, DWORD reason, LPVOID reserved) {
     InitializeCrashReportingForProcess();
     // CRT on initialization installs an exception filter which calls
     // TerminateProcess. We need to hook CRT's attempt to set an exception
-    // handler and ignore it.
+    // handler and ignore it. Don't do this when ASan is present, or ASan will
+    // fail to install its own unhandled exception filter.
+#if !defined(ADDRESS_SANITIZER)
     DisableSetUnhandledExceptionFilter();
+#endif
 
     install_static::InitializeProcessType();
     if (install_static::g_process_type ==