Fix inconsistent keyboard focus style in quick view buttons.

Updated the open file button's outline to be consistent with the
outline of metadata box toggle button.

TEST=manually.
BUG=663669
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2623413002
Cr-Commit-Position: refs/heads/master@{#443169}

ui/file_manager/file_manager/foreground/elements/files_quick_view.css

@@ -29,7 +29,7 @@ paper-dialog {
 }
 
 paper-button:focus:not(:active) {
-  box-shadow: 0 0 0 2px rgba(191, 191, 191, 0.5);
+  box-shadow: 0 0 0 1px rgba(66, 133, 244, 0.5);
 }
 
 #audio-artwork {