[android-webview] Skip signal handler registration on x86/64

An intricate entangling of libsigchain, sigaction() chaining and
user-space SIGSEGV handling by binary translator cause persistent
crashes when a SIGSEGV handler is installed by a x86 library on
a hybrid application which uses both Arm and x86 libraries.
Backing out the crash handler as a temporary workaround.
More context in the related bug.

BUG=477444

Review URL: https://codereview.chromium.org/1059543003

Cr-Commit-Position: refs/heads/master@{#325441}

android_webview/common/aw_crash_handler.cc

@@ -11,6 +11,7 @@
 #include <unistd.h>
 
 #include "base/logging.h"
+#include "build/build_config.h"
 
 namespace {
 
@@ -66,6 +67,13 @@ namespace android_webview {
 namespace crash_handler {
 
 void RegisterCrashHandler(const std::string& version) {
+#if defined(ARCH_CPU_X86_FAMILY)
+  // Don't install signal handler on X86/64 because this breaks binary
+  // translators that handle SIGSEGV in userspace and get chained after our
+  // handler. See crbug.com/477444
+  return;
+#endif
+
   if (crash_handler_registered) {
     NOTREACHED();
     return;