Add --use-more-webui runtime flag to toggle WebUI replacements for native dialogs.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 89824b323be26708d161e7565697e70eac685e97..e286862af19da29f91ee3910516d5f0fb76433aa 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -35,11 +35,6 @@
           # Disable touch support by default.
           'touchui%': 0,
 
-          # Disable webui dialog replacements for native dialogs by default.
-          # TODO(flackr): Change this to a runtime flag triggered by
-          #     --pure-views so that these dialogs can be easily tested. 
-          'webui_dialogs%': 0,
-
           # Whether the compositor is enabled on views.
           'views_compositor%': 0,
         },
@@ -47,7 +42,6 @@
         'chromeos%': '<(chromeos)',
         'toolkit_uses_pure_views%': '<(toolkit_uses_pure_views)',
         'touchui%': '<(touchui)',
-        'webui_dialogs%': '<(webui_dialogs)',
         'views_compositor%': '<(views_compositor)',
 
         # Compute the architecture that we're building on.
@@ -76,18 +70,12 @@
           }, {
             'toolkit_uses_pure_views%': 0,
           }],
-
-          # Use WebUI dialogs in TouchUI builds.
-          ['touchui==1', {
-            'webui_dialogs%': 1,
-          }],
         ],
       },
 
       # Copy conditionally-set variables out one scope.
       'chromeos%': '<(chromeos)',
       'touchui%': '<(touchui)',
-      'webui_dialogs%': '<(webui_dialogs)',
       'host_arch%': '<(host_arch)',
       'toolkit_views%': '<(toolkit_views)',
       'toolkit_uses_pure_views%': '<(toolkit_uses_pure_views)',
@@ -294,7 +282,6 @@
     'enable_flapper_hacks%': '<(enable_flapper_hacks)',
     'chromeos%': '<(chromeos)',
     'touchui%': '<(touchui)',
-    'webui_dialogs%': '<(webui_dialogs)',
     'file_manager_extension%': '<(file_manager_extension)',
     'webui_task_manager%': '<(webui_task_manager)',
     'inside_chromium_build%': '<(inside_chromium_build)',
@@ -666,9 +653,6 @@
       ['touchui==1', {
         'grit_defines': ['-D', 'touchui'],
       }],
-      ['webui_dialogs==1', {
-        'grit_defines': ['-D', 'webui_dialogs'],
-      }],
       ['file_manager_extension==1', {
         'grit_defines': ['-D', 'file_manager_extension'],
       }],