[runtime] Cleanup native methods creation in debug/debug.js and debug/mirrors.js.

This CL replaces usages of utils.InstallFunctions and utils.InstallGetter()
with utils.InstallConstants(). Since these methods are not exposed to the user it
doesn't matter if we add them with DONT_ENUM attributes or not.

This CL is one of a series of cleanup CL which are the preliminary steps for
improving function closures creation.

Bug: v8:6459
Change-Id: I41708741f1cc013e4f4c37f1c7a73c1333deca7d
Reviewed-on: https://chromium-review.googlesource.com/548137
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46288}

src/debug/debug.js

@@ -1000,7 +1000,7 @@ utils.InstallConstants(global, [
 ]);
 
 // Functions needed by the debugger runtime.
-utils.InstallFunctions(utils, DONT_ENUM, [
+utils.InstallConstants(utils, [
   "MakeExecutionState", MakeExecutionState,
   "MakeExceptionEvent", MakeExceptionEvent,
   "MakeBreakEvent", MakeBreakEvent,

src/debug/mirrors.js

@@ -2364,11 +2364,8 @@ ContextMirror.prototype.data = function() {
 // ----------------------------------------------------------------------------
 // Exports
 
-utils.InstallFunctions(global, DONT_ENUM, [
-  "MakeMirror", MakeMirror,
-]);
-
 utils.InstallConstants(global, [
+  "MakeMirror", MakeMirror,
   "ScopeType", ScopeType,
   "PropertyType", PropertyType,
   "PropertyAttribute", PropertyAttribute,