Fixes uncaught exception in memory plugin on IE6/7

The memory plugin uses document.getElementsByTagName in order to count
the number of certain types of DOM elements. It uses (function).call() to
do this. In IE6/7 the getElementsByTagName is not a typical function and
does not have call(). This patch wraps the underlying function in an
anonymous function when call() is missing.
(cherry picked from commit 2eb2a6e)

Signed-off-by: Philip Tellis <philip.tellis@gmail.com>

plugins/memory.js

@@ -19,13 +19,17 @@ BOOMR.plugins = BOOMR.plugins || {};
 var impl = {
 	complete: false,
 	done: function() {
-		var w = BOOMR.window,
-		    p = w.performance,
-		    c = w.console,
-		    d = w.document,
-		    f = (({}).toString.call(w.opera) == '[object Opera]' ? d.querySelectorAll : d.getElementsByTagName),
+		var w  = BOOMR.window,
+		    p  = w.performance,
+		    c  = w.console,
+		    d  = w.document,
+		    _f = (({}).toString.call(w.opera) == '[object Opera]' ? d.querySelectorAll : d.getElementsByTagName),
 		    m;
 
+		// handle IE6/7 weirdness regarding host objects
+		// See: http://stackoverflow.com/questions/7125288/what-is-document-getelementbyid
+		var f  = (typeof _f.call === 'undefined' ? function(tag) { return _f(tag) } : _f);
+
 		m = (p && p.memory ? p.memory : (c && c.memory ? c.memory : null));
 
 		if(m) {
@@ -35,13 +39,13 @@ var impl = {
 			});
 		}
 
-		
+
 		BOOMR.addVar({
 			'dom.ln': f.call(d, '*').length,
 			'dom.sz': f.call(d, 'html')[0].innerHTML.length,
 			'dom.img': f.call(d, 'img').length,
 			'dom.script': f.call(d, 'script').length
-		}); 
+		});
 
 		this.complete = true;
 		BOOMR.sendBeacon();