[v8][macosx] Use V8's default wasm trap handler on MacOS

This CL enables WebAssembly trap handlers on MacOS. In this CL we use
the default trap handler provided by V8.

Bug: chromium:906565

Change-Id: I2d007da1a86ca05010a0a7bf830586767f19a24d
Reviewed-on: https://chromium-review.googlesource.com/c/1290955
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609942}

chrome/test/v8/wasm_trap_handler_browsertest.cc

@@ -25,6 +25,8 @@ namespace {
 constexpr bool kIsTrapHandlerSupported = true;
 #elif defined(OS_WIN) && defined(ARCH_CPU_X86_64)
 constexpr bool kIsTrapHandlerSupported = true;
+#elif defined(OS_MACOSX) && defined(ARCH_CPU_X86_64)
+constexpr bool kIsTrapHandlerSupported = true;
 #else
 constexpr bool kIsTrapHandlerSupported = false;
 #endif

content/renderer/render_process_impl.cc

@@ -197,6 +197,15 @@ RenderProcessImpl::RenderProcessImpl(
     v8::V8::EnableWebAssemblyTrapHandler(use_v8_trap_handler);
   }
 #endif
+#if defined(OS_MACOSX) && defined(ARCH_CPU_X86_64)
+  if (base::FeatureList::IsEnabled(features::kWebAssemblyTrapHandler)) {
+    // On macOS, Crashpad uses exception ports to handle signals in a different
+    // process. As we cannot just pass a callback to this other process, we ask
+    // V8 to install its own signal handler to deal with WebAssembly traps.
+    bool use_v8_signal_handler = true;
+    v8::V8::EnableWebAssemblyTrapHandler(use_v8_signal_handler);
+  }
+#endif  // defined(OS_MACOSX) && defined(ARCH_CPU_X86_64)
 
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();