dedup script source before evaluating it in the sandbox

strings sent via e10s message manager are duplicated and the sandbox
holds onto them as source code, this causes unnecessary memory overhead.

content/framescript.js

@@ -79,6 +79,7 @@ function createScriptFromObject(aObject) {
   for (var key in aObject) {
     script[key] = aObject[key];
   }
+  script.dedup();
   return script;
 };
 

modules/ipcscript.js

@@ -3,6 +3,8 @@ var EXPORTED_SYMBOLS = ['IPCScript'];
 Components.utils.import("chrome://greasemonkey-modules/content/extractMeta.js");
 Components.utils.import("chrome://greasemonkey-modules/content/util.js");
 
+var instances = new Map();
+
 function IPCScript(aScript, addonVersion) {
   this.addonVersion = addonVersion;
   this.description = aScript.description;
@@ -48,6 +50,21 @@ function IPCScript_getMetaStr() {
   return this._metaStr;
 });
 
+IPCScript.prototype.dedup = function() {
+  // scripts sent via e10s message manager contain new string instances every time a new one is created -> dedup them to reduce memory footprint
+
+  // alternative approaches:
+  // a) beam down IPC script instances only once via the parent process manager every time they change.
+  // b) creating resource URIs and loading user scripts straight from URIs might also be more elegant
+  //    see: https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Using#Programmatically_adding_aliases
+  var old = instances.get(this.uuid);
+
+  if(old == this.textContent)
+    this.textContent = old
+  else
+    instances.set(this.uuid, this.textContent)
+};
+
 IPCScript.prototype.info = function() {
   var resources = {};
   for (var i = 0, r = null; r = this.resources[i]; i++) {
@@ -80,4 +97,4 @@ IPCScript.prototype.info = function() {
       'version': this.version
     }
   };
-};
+};

modules/sandbox.js

@@ -34,9 +34,8 @@ function createSandbox(aScript, aContentWin, aUrl, aFrameScope) {
           'wantXrays': false,
         });
     // GM_info is always provided.
-    // TODO: lazy getter? XPCOMUtils.defineLazyGetter
-    Components.utils.evalInSandbox(
-        'const GM_info = ' + uneval(aScript.info()), contentSandbox);
+    injectGMInfo(aScript, contentSandbox);
+
     // Alias unsafeWindow for compatibility.
     Components.utils.evalInSandbox(
         'const unsafeWindow = window;', contentSandbox);
@@ -122,14 +121,37 @@ function createSandbox(aScript, aContentWin, aUrl, aFrameScope) {
         'contentStartRequest');
   }
 
-  // TODO: lazy getter?
-  Components.utils.evalInSandbox(
-      'const GM_info = ' + uneval(aScript.info()), sandbox);
+  injectGMInfo(aScript, sandbox)
 
   return sandbox;
 }
 
 
+function injectGMInfo(aScript, sandbox) {
+  // info contains scriptSource, which can be quite large and would get cloned into every tab
+  // to avoid the memory overhead we only clone the lightweight properties into the sandbox
+  // and define a getter for the scriptSource instead
+  var rawInfo = aScript.info();
+  var infoProxy = {}
+  for(var key in Object.keys(rawInfo)) {
+    if(key == "scriptSource")
+      continue;
+    infoProxy[key] = rawInfo[key]
+  }
+
+  // TODO: also delay top level clone via lazy getter? XPCOMUtils.defineLazyGetter
+  sandbox.GM_info = Cu.cloneInto(infoProxy, sandbox);
+
+  var waivedSandbox = Components.utils.waiveXrays(sandbox)
+
+  waivedSandbox.Object.defineProperty(sandbox.GM_info,
+    "scriptSource",
+    { get: Cu.exportFunction(function() {return rawInfo.scriptSource}, sandbox)
+  });  
+}
+
+
+
 function runScriptInSandbox(script, sandbox) {
   // Eval the code, with anonymous wrappers when/if appropriate.
   function evalWithWrapper(code, fileName) {