Upstream "nsurl_util.{h,mm}" from Chrome on iOS repository.

I created the new directory net/base/mac/ to hold shared files between OSX and
iOS. The logic in nsurl_util was mostly duplicated code, so I replaced the bulk
of the code with a single new function EscapeNSURLPrecursor.

BUG=

Review URL: https://codereview.chromium.org/747773002

Cr-Commit-Position: refs/heads/master@{#306690}
diff --git a/net/net.gyp b/net/net.gyp
index 5ddf4307..8bfcc7b 100644
--- a/net/net.gyp
+++ b/net/net.gyp
@@ -442,6 +442,12 @@
             },
           },
         ],
+        [ 'OS == "ios" or OS == "mac"', {
+            'sources': [
+              '<@(net_base_mac_ios_sources)',
+            ],
+          },
+        ],
         ['OS=="android" and _toolset=="target" and android_webview_build == 0', {
           'dependencies': [
              'net_java',
@@ -550,6 +556,11 @@
             '<@(net_linux_test_sources)',
           ],
         }],
+        ['OS == "mac" or OS == "ios"', {
+          'sources': [
+            '<@(net_base_test_mac_ios_sources)',
+          ],
+        }],
         ['chromeos==1', {
           'sources!': [
             'proxy/proxy_config_service_linux_unittest.cc',