Description: Replace layout constants in chrome/browser/extensions and chrome/browser/first_run

Changes in this patch as below:
1. Replace references to constants in ui/views/layout/layout_constants.h with their
   equivalents using ChromeLayoutProvider.

2. Changed the RequestFileSystemDialogView class to use a simpler FillLayout instead of
   a BoxLayout. This class now subclasses DialogDelegateView instead of DialogDelegate for
   simplicity. Removed the dependency on Extension and Volume datatypes from this class, which
   enables us to easily test the dialog. The extension name, volume label and id are passed in.
   We maintain the contract of invoking the cancel callback if the volume label is empty. That is
   done in the caller ConsentProviderDelegate::ShowDialog().

3. Added browser tests for displaying the TryChromeDialogView and RequestFileSystemDialogView dialogs.

4. Made the TryChromeDialogTest class a friend of the TryChromeDialogView class. This allows it to
   instantiate an instance of this class. The TryChromeDialogView class no longer puts up a modal
   dialog by default. This is controlled by the DialogType enum, which for chrome is always MODAL.
   For the browser tests we pass in MODELESS here, as the loop is run by the test. The ShowModal() method
   is renamed to ShowDialog(). It takes an additional enum UsageType which controls whether we are in testing
   mode. In this case we always want the dialog to be displayed.

BUG=691897
TEST=Covered by tests RequestFileSystemDialogTest.InvokeDialog_default and TryChromeDialogTest.InvokeDialog_default
TBR=grt

Review-Url: https://codereview.chromium.org/2816293002
Cr-Commit-Position: refs/heads/master@{#468195}
diff --git a/chrome/browser/DEPS b/chrome/browser/DEPS
index cb576af5..f671795 100644
--- a/chrome/browser/DEPS
+++ b/chrome/browser/DEPS
@@ -74,6 +74,8 @@
   "-chrome/browser/ui/views",
   "+chrome/browser/ui/views/chrome_browser_main_extra_parts_views.h",
   "+chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.h",
+  "+chrome/browser/ui/views/extensions/request_file_system_dialog_view.h",
+  "+chrome/browser/ui/views/try_chrome_dialog_view.h",
   "+chrome/browser/ui/views/ash/chrome_browser_main_extra_parts_ash.h",
 
   # Code in chrome should not use ash::SessionStateDelegate and friends.