Fix padding in home page settings.

The "on"/"off" text and the switch were both too close to the edge of
the screen on pre-L devices. The bug arose because the LinearLayout had
conflicting padding attributes: it defined "padding" inline, and used a
style which defined "paddingStart" and "paddingEnd". The latter values
were overriding the inline "padding" value.

Review URL: https://codereview.chromium.org/970603003

Cr-Commit-Position: refs/heads/master@{#319011}

chrome/android/java/res/layout/homepage_preferences.xml

@@ -20,7 +20,10 @@
             android:layout_height="wrap_content"
             android:gravity="center_vertical"
             android:orientation="horizontal"
-            android:padding="16dp"
+            android:paddingStart="16dp"
+            android:paddingEnd="16dp"
+            android:paddingTop="16dp"
+            android:paddingBottom="16dp"
             style="@style/PreferenceLayout" >
 
             <TextView