Add sample extension that allows setting plugin-specific content settings.

chrome/common/extensions/docs/examples/extensions/plugin_settings/domui/css/list.css

Index: chrome/common/extensions/docs/examples/extensions/plugin_settings/domui/css/list.css
diff --git a/chrome/common/extensions/docs/examples/extensions/plugin_settings/domui/css/list.css b/chrome/common/extensions/docs/examples/extensions/plugin_settings/domui/css/list.css
new file mode 100644
index 0000000000000000000000000000000000000000..75d2a9294720e2e375bb469467c6579d7a600655
--- /dev/null
+++ b/chrome/common/extensions/docs/examples/extensions/plugin_settings/domui/css/list.css
@@ -0,0 +1,89 @@
+
+list,
+grid {
+  display: block;
+  outline: none;
+  overflow: auto;
+  position: relative; /* Make sure that item offsets are relative to the
+                         list. */
+}
+
+list > *,
+grid > * {
+  -webkit-user-select: none;
+  background-color: rgba(255,255,255,0);
+  border: 1px solid rgba(255,255,255,0); /* transparent white */
+  border-radius: 2px;
+  cursor: default;
+  line-height: 20px;
+  margin: -1px 0;
+  overflow: hidden;
+  padding: 0px 3px;
+  position: relative; /* to allow overlap */
+  text-overflow: ellipsis;
+  white-space: pre;
+}
+
+list > * {
+  display: block;
+}
+
+grid > * {
+  display: inline-block;
+}
+
+list > [lead],
+grid > [lead] {
+  border-color: transparent;
+}
+
+list:focus > [lead],
+grid:focus > [lead] {
+  border-color: hsl(214, 91%, 65%);
+  z-index: 2;
+}
+
+list > [anchor],
+grid > [anchor] {
+
+}
+
+list:not([disabled]) > :hover,
+grid:not([disabled]) > :hover {
+  border-color: hsl(214, 91%, 85%);
+  z-index: 1;
+  background-color: hsl(214, 91%, 97%);
+}
+
+list > [selected],
+grid > [selected] {
+  border-color: hsl(0, 0%, 85%);
+  background-color: hsl(0,0%,90%);
+  z-index: 2;
+  background-image: -webkit-linear-gradient(rgba(255, 255, 255, 0.8),
+                                            rgba(255, 255, 255, 0));
+}
+
+list:focus > [selected],
+grid:focus > [selected] {
+  background-color: hsl(214,91%,89%);
+  border-color: hsl(214, 91%, 65%);
+}
+
+list:focus > [lead][selected],
+list > [selected]:hover,
+grid:focus > [lead][selected],
+grid > [selected]:hover {
+  background-color: hsl(214, 91%, 87%);
+  border-color: hsl(214, 91%, 65%);
+}
+
+list > .spacer,
+grid > .spacer {
+  border: 0;
+  box-sizing: border-box;
+  display: block;
+  overflow: hidden;
+  visibility: hidden;
+  margin: 0;
+}