Bug 1445973: Part 2: Add 'clearSavedFrames' testing function to JS shell. r=jorendorff

OOM tests often depend on invoking a function repeatedly, failing a different
allocation each time. Flushing the caches helps ensure consistent behavior from
one invocation to the next.

--HG--
extra : rebase_source : 0bf4a46c7c3e0bceb0fe77bbf96e422558a988c4
extra : source : 1a11067ab1e6b62602b79081e3208dcad31807bd

js/src/builtin/TestingFunctions.cpp

@@ -1241,6 +1241,23 @@ GetSavedFrameCount(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
+static bool
+ClearSavedFrames(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    js::SavedStacks& savedStacks = cx->compartment()->savedStacks();
+    if (savedStacks.initialized())
+        savedStacks.clear();
+
+    for (ActivationIterator iter(cx); !iter.done(); ++iter) {
+        iter->clearLiveSavedFrameCache();
+    }
+
+    args.rval().setUndefined();
+    return true;
+}
+
 static bool
 SaveStack(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -5170,6 +5187,12 @@ static const JSFunctionSpecWithHelp TestingFunctions[] = {
 "  Return the number of SavedFrame instances stored in this compartment's\n"
 "  SavedStacks cache."),
 
+    JS_FN_HELP("clearSavedFrames", ClearSavedFrames, 0, 0,
+"clearSavedFrames()",
+"  Empty the current compartment's cache of SavedFrame objects, so that\n"
+"  subsequent stack captures allocate fresh objects to represent frames.\n"
+"  Clear the current stack's LiveSavedFrameCaches."),
+
     JS_FN_HELP("saveStack", SaveStack, 0, 0,
 "saveStack([maxDepth [, compartment]])",
 "  Capture a stack. If 'maxDepth' is given, capture at most 'maxDepth' number\n"