Implicit stack overflow checks and null checks are the norm now.

Make the default to true so that unit tests don't need to
use the full CompilerOptions constructor.

Change-Id: Ieb52235af73dce2fa03f12932e22ebe2294c805b
diff --git a/compiler/driver/compiler_options.h b/compiler/driver/compiler_options.h
index 97699e5..5466d45 100644
--- a/compiler/driver/compiler_options.h
+++ b/compiler/driver/compiler_options.h
@@ -64,8 +64,8 @@
     include_patch_information_(kDefaultIncludePatchInformation),
     top_k_profile_threshold_(kDefaultTopKProfileThreshold),
     include_debug_symbols_(kDefaultIncludeDebugSymbols),
-    implicit_null_checks_(false),
-    implicit_so_checks_(false),
+    implicit_null_checks_(true),
+    implicit_so_checks_(true),
     implicit_suspend_checks_(false),
     compile_pic_(false),
     verbose_methods_(nullptr),