Skip calculating SRI for assets from the public/ folder.

Saves on average ~2ms per file in one app, which adds up when there are
hundreds. SRI is currently only supported for js and css files, and Meteor
only uses it for the main bundles.

tools/isobuild/bundler.js

@@ -546,6 +546,9 @@ class File {
     // disk).
     this.sourcePath = options.sourcePath;
 
+    // Allows not calculating sri when the file doesn't support it
+    this._skipSri = options.skipSri
+
     // info is just for help with debugging the tool; it isn't written to disk or
     // anything.
     this.info = options.info || '?';
@@ -619,7 +622,9 @@ class File {
         hashes.push(this._inputHash);
       }
 
-      hashes.push(this.sri());
+      if (!this._skipSri) {
+        hashes.push(this.sri());
+      }
 
       this._hash = watch.sha1(...hashes);
     }
@@ -628,7 +633,7 @@ class File {
   }
 
   sri() {
-    if (! this._sri) {
+    if (! this._sri && !this._skipSri) {
       this._sri = watch.sha512(this.contents());
     }
 
@@ -1160,6 +1165,8 @@ class Target {
           data: resource.data,
           cacheable: false,
           hash: resource.hash,
+          sourcePath: resource.sourcePath,
+          skipSri: !!resource.sourcePath && resource.hash
         };
 
         const file = new File(fileOptions);

tools/isobuild/compiler.js

@@ -457,7 +457,7 @@ var compileUnibuild = Profile(function (options) {
 
   // This function needs to be factored out to support legacy handlers later on
   // in the compilation process
-  function addAsset(contents, relPath, hash) {
+  function addAsset(contents, relPath, absPath, hash) {
     // XXX hack to strip out private and public directory names from app asset
     // paths
     if (! inputSourceArch.pkg.name) {
@@ -470,7 +470,8 @@ var compileUnibuild = Profile(function (options) {
       path: relPath,
       servePath: colonConverter.convert(
         files.pathJoin(inputSourceArch.pkg.serveRoot, relPath)),
-      hash: hash
+      hash: hash,
+      sourcePath: absPath
     });
   }
 
@@ -482,7 +483,7 @@ var compileUnibuild = Profile(function (options) {
     const hash = optimisticHashOrNull(absPath)
     const contents = optimisticReadFile(absPath)
 
-    addAsset(contents, relPath, hash);
+    addAsset(contents, relPath, absPath, hash);
   });
 
   // Add and compile all source files