Use String::indexOf instead of String::startsWith

String::startsWith isn't available in the browser process yet.

src/package-manager.coffee

@@ -228,7 +228,7 @@ class PackageManager
     packages = []
     for packagePath in @getAvailablePackagePaths()
       name = path.basename(packagePath)
-      metadata = @getLoadedPackage(name)?.metadata ? Package.loadMetadata(packagePath, true)
+      metadata = @getLoadedPackage(name)?.metadata ? Package.loadMetadata(packagePath, {ignoreErrors: true, @resourcePath, @devMode})
       packages.push(metadata)
     packages
 
@@ -252,7 +252,7 @@ class PackageManager
     @packageDependencies
 
   hasAtomEngine: (packagePath) ->
-    metadata = Package.loadMetadata(packagePath, true)
+    metadata = Package.loadMetadata(packagePath, ignoreErrors: true)
     metadata?.engines?.atom?
 
   unobserveDisabledPackages: ->

src/package.coffee

@@ -26,16 +26,19 @@ class Package
 
   @stylesheetsDir: 'stylesheets'
 
-  @isBundledPackagePath: (packagePath) ->
-    if atom.packages.devMode
-      return false unless atom.packages.resourcePath.startsWith("#{process.resourcesPath}#{path.sep}")
+  @isBundledPackagePath: (packagePath, resourcePath, devMode) ->
+    resourcePath ?= atom?.packages.resourcePath
+    devMode ?= atom?.packages.devMode
 
-    @resourcePathWithTrailingSlash ?= "#{atom.packages.resourcePath}#{path.sep}"
-    packagePath?.startsWith(@resourcePathWithTrailingSlash)
+    if devMode
+      return false unless resourcePath.indexOf("#{process.resourcesPath}#{path.sep}") is 0
 
-  @loadMetadata: (packagePath, ignoreErrors=false) ->
+    @resourcePathWithTrailingSlash ?= "#{resourcePath}#{path.sep}"
+    packagePath?.indexOf(@resourcePathWithTrailingSlash) is 0
+
+  @loadMetadata: (packagePath, {ignoreErrors, devMode, resourcePath}={}) ->
     packageName = path.basename(packagePath)
-    if @isBundledPackagePath(packagePath)
+    if @isBundledPackagePath(packagePath, resourcePath, devMode)
       metadata = packagesCache[packageName]?.metadata
     unless metadata?
       if metadataPath = CSON.resolve(path.join(packagePath, 'package'))