ui: Have shell_dialogs into its own gyp file under its shell_dialogs/ directory.

chrome/chrome.gyp

Index: chrome/chrome.gyp
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index 1e279c0165c6997b38013bff572bfdf96f59cec2..5bd5d433e21debfa35a29ebeae80430614af6f20 100644
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -831,7 +831,7 @@
             '../content/content_shell_and_tests.gyp:content_shell',
             '../content/content_shell_and_tests.gyp:content_unittests',
             '../net/net.gyp:net_unittests',
-            '../ui/ui.gyp:ui_unittests',
+            '../ui/ui_unittests.gyp:ui_unittests',
           ],
           'conditions': [
             ['use_aura==1 or target_arch=="x64"', {