Add support for building "ios_chrome_unittests" with gn.

ios/web/js_compile.gni

Index: ios/web/js_compile.gni
diff --git a/ios/web/js_compile.gni b/ios/web/js_compile.gni
index 6c9590af12af909a3d4445127d863b366ef1febe..a8c70713650d415cb574bc2b4546a7ed9234798c 100644
--- a/ios/web/js_compile.gni
+++ b/ios/web/js_compile.gni
@@ -30,7 +30,8 @@ closure_compiler_path = "//third_party/closure_compiler/compiler/compiler.jar"
 # Generates a single JavaScript bundle file that can be put in the application
 # bundle.
 #
-# TODO(eugenebut): this should uses the same error flags as js_compile_checked.
+# TODO(crbug.com/487804): once all errors have been fixed, sync with the flags
+# from third_party/closure_compiler/closure_args.gni.
 template("js_compile_bundle") {
   assert(defined(invoker.sources),
          "Need sources in $target_name listing the js files.")
@@ -86,8 +87,8 @@ template("js_compile_bundle") {
 #   visibility (optional)
 #     Visibility restrictions.
 #
-# TODO(eugenebut): use flags from third_party/closure_compiler/closure_args.gni
-# once they are the same.
+# TODO(crbug.com/487804): once all errors have been fixed, sync with the flags
+# from third_party/closure_compiler/closure_args.gni.
 template("js_compile_checked") {
   assert(defined(invoker.sources),
          "Need sources in $target_name listing the js files.")
@@ -106,8 +107,8 @@ template("js_compile_checked") {
         "$target_gen_dir/{{source_file_part}}",
       ]
 
-      # TODO(eugenebut): need to enable the following compilation checks once
-      # the corresponding errors have been fixed:
+      # TODO(crbug.com/487804): need to enable the following compilation checks
+      # once the corresponding errors have been fixed:
       #   --jscomp_error=checkTypes
       #   --jscomp_error=checkVars
       #   --jscomp_error=missingProperties
@@ -169,3 +170,79 @@ template("js_compile_checked") {
     }
   }
 }
+
+# Defines a target that compile JavaScript files without error checking using
+# the closure compiler.
+#
+# Variables
+#   sources:
+#     List of JavaScript files to compile.
+#
+#   deps (optional)
+#     List of targets required by this target.
+#
+#   visibility (optional)
+#     Visibility restrictions.
+#
+# TODO(crbug.com/487804): once all errors have been fixed, remove this template
+# and port all code to use js_compile_checked instead.
+template("js_compile_unchecked") {
+  assert(defined(invoker.sources),
+         "Need sources in $target_name listing the js files.")
+
+  if (compile_javascript) {
+    java_action_foreach(target_name) {
+      forward_variables_from(invoker,
+                             [
+                               "deps",
+                               "visibility",
+                             ])
+
+      script = closure_compiler_path
+      sources = invoker.sources
+      outputs = [
+        "$target_gen_dir/{{source_file_part}}",
+      ]
+
+      args = [
+        "--compilation_level",
+        "SIMPLE_OPTIMIZATIONS",
+        "--js",
+        "{{source}}",
+        "--js_output_file",
+        rebase_path("$target_gen_dir/{{source_file_part}}", root_build_dir),
+      ]
+
+      # TODO(crbug.com/546283): add the generated bundle to the list of files
+      # to move in the application bundle, equivalent to the following gyp code:
+      #
+      # "link_settings": {
+      #   "mac_bundle_resources": [
+      #     "<(SHARED_INTERMEDIATE_DIR)/<(RULE_INPUT_NAME).js",
+      #   ],
+      # },
+    }
+  } else {
+    copy(target_name) {
+      forward_variables_from(invoker,
+                             [
+                               "deps",
+                               "visibility",
+                             ])
+
+      sources = invoker.sources
+      outputs = [
+        "$target_gen_dir/{{source_file_part}}",
+      ]
+
+      # TODO(crbug.com/546283): add the generated bundle to the list of files
+      # to move in the application bundle, equivalent to the following gyp code:
+      #
+      # "link_settings": {
+      #   "mac_bundle_resources": [
+      #     "<(SHARED_INTERMEDIATE_DIR)/<(RULE_INPUT_NAME).js",
+      #   ],
+      # },
+    }
+  }
+}