[wasm] Turn on trap handler by default on Linux

After more than half a year of finch trial we can turn
WebAssembly trap handler on Linux on by default.

R=titzer@chromium.org, hablich@chromium.org, piman@chromium.org

Bug: chromium:722585
Change-Id: Id52754dba6d80ce794e350216b9a0c0d93c76ebd
Reviewed-on: https://chromium-review.googlesource.com/c/1322872Reviewed-by: Michael Hablich <hablich@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607194}

content/public/common/content_features.cc

@@ -472,8 +472,13 @@ const base::Feature kWebAssemblyThreads{"WebAssemblyThreads",
                                         base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enable WebAssembly trap handler.
+#if defined(OS_LINUX) && defined(ARCH_CPU_X86_64)
+const base::Feature kWebAssemblyTrapHandler{"WebAssemblyTrapHandler",
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
+#else
 const base::Feature kWebAssemblyTrapHandler{"WebAssemblyTrapHandler",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
+#endif
 
 // Controls whether the visibility of a WebContents can be OCCLUDED. When
 // disabled, an occluded WebContents behaves exactly like a VISIBLE WebContents.