Deactivate webgl in iOS UIWebView to avoid crash

Author: pandamicro

CCBoot.js

@@ -1859,10 +1859,17 @@ var _initSys = function () {
         var tmpCanvas = document.createElement("CANVAS");
         try{
             var context = cc.create3DContext(tmpCanvas, {'stencil': true});
-            if(context) {
+            if (context && context.getShaderPrecisionFormat) {
                 _supportWebGL = true;
             }
 
+            if (_supportWebGL && sys.os === sys.OS_IOS) {
+                // Not activating WebGL in iOS UIWebView because it may crash when entering background
+                if (!window.indexedDB) {
+                    _supportWebGL = false;
+                }
+            }
+
             if (_supportWebGL && sys.os === sys.OS_ANDROID) {
                 var browserVer = parseFloat(sys.browserVersion);
                 switch (sys.browserType) {