A simple, practically zero cost fallback crash handler for Crashpad handler process.

components/crash/content/app/BUILD.gn

Index: components/crash/content/app/BUILD.gn
diff --git a/components/crash/content/app/BUILD.gn b/components/crash/content/app/BUILD.gn
index 4bdcc707212ee9d13333fa796d2dac83eed4a352..7552646936c5e62055f5d7ea60375a565472f270 100644
--- a/components/crash/content/app/BUILD.gn
+++ b/components/crash/content/app/BUILD.gn
@@ -66,6 +66,8 @@ if (is_win) {
     sources = [
       "crash_switches.cc",
       "crash_switches.h",
+      "fallback_crash_handler_launcher_win.cc",
+      "fallback_crash_handler_launcher_win.h",
       "run_as_crashpad_handler_win.cc",
       "run_as_crashpad_handler_win.h",
     ]
@@ -213,15 +215,20 @@ source_set("unit_tests") {
   testonly = true
   sources = [
     "crash_keys_win_unittest.cc",
+    "fallback_crash_handler_launcher_win_unittest.cc",
   ]
   deps = [
     ":lib",
     "//base",
+    "//base/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 
   if (is_win) {
-    deps += [ "//breakpad:client" ]
+    deps += [
+      ":run_as_crashpad_handler",
+      "//breakpad:client",
+    ]
   }
 }