Bug 944975: cleanup rename JSScript originalFunction to donorFunction (r=shu).

The motivation here is to distinguish the two kinds of methods: one
that assumes the receiver is a clone versus another that assumes
nothing about the receiver. I.e., something along the lines of:

  clone.originalFunction() == clone.donorFunction()
  nonclone.donorFunction() == null
  nonclone.originalFunction() == nonclone

js/src/jit/BaselineJIT.cpp

@@ -285,7 +285,7 @@ CanEnterBaselineJIT(JSContext *cx, HandleScript script, bool osr)
     if (script->isCallsiteClone()) {
         // Ensure the original function is compiled too, so that bailouts from
         // Ion code have a BaselineScript to resume into.
-        RootedScript original(cx, script->originalFunction()->nonLazyScript());
+        RootedScript original(cx, script->donorFunction()->nonLazyScript());
         JS_ASSERT(original != script);
 
         if (!original->canBaselineCompile())

js/src/jsfun.h

@@ -339,11 +339,11 @@ class JSFunction : public JSObject
         return u.i.s.script_;
     }
 
-    // Returns the non-callsited-clone version of this function.  Use
-    // when return-value can flow to arbitrary JS (see Bug 944975).
+    // Returns non-callsited-clone version of this.  Use when return
+    // value can flow to arbitrary JS (see Bug 944975).
     JSFunction* originalFunction() {
         if (this->hasScript() && this->nonLazyScript()->isCallsiteClone()) {
-            return this->nonLazyScript()->originalFunction();
+            return this->nonLazyScript()->donorFunction();
         } else {
             return this;
         }

js/src/jsscript.h

@@ -1273,7 +1273,10 @@ class JSScript : public js::gc::BarrieredCell<JSScript>
      */
     inline void ensureNonLazyCanonicalFunction(JSContext *cx);
 
-    JSFunction *originalFunction() const;
+    /*
+     * Donor provided itself to callsite clone; null if this is non-clone.
+     */
+    JSFunction *donorFunction() const;
     void setIsCallsiteClone(JSObject *fun);
 
     JSFlatString *sourceData(JSContext *cx);

js/src/jsscriptinlines.h

@@ -149,7 +149,7 @@ JSScript::principals()
 }
 
 inline JSFunction *
-JSScript::originalFunction() const {
+JSScript::donorFunction() const {
     if (!isCallsiteClone())
         return nullptr;
     return &enclosingScopeOrOriginalFunction_->as<JSFunction>();