[Android] PhotoPicker: Rounded edges for the SeekBar.

This changes the SeekBar to have rounded edges.

Screenshot: https://crbug.com/895776#c57
Bug: 895776, 656015
Change-Id: I440a539d9f80af53e672afd65927cff9cf40a13b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250184
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780343}

chrome/android/java/res/drawable/photo_picker_seekbar_track.xml

@@ -13,21 +13,28 @@
 The buffering progress line (item 2 above) is omitted here, because it is not needed due to the fact
 that the videos are all readily available on disk and don't need to be downloaded. -->
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:id="@android:id/background">
-        <shape android:shape="line">
-            <stroke
-                android:color="@color/modern_grey_500"
-                android:width="@dimen/photo_picker_seek_bar_thickness" />
+    <item android:id="@android:id/background"
+        android:gravity="center_vertical|fill_horizontal">
+        <shape android:shape="rectangle">
+            <corners android:radius="@dimen/photo_picker_seek_bar_edge_radius" />
+            <size android:height="@dimen/photo_picker_seek_bar_thickness" />
+            <gradient
+                android:angle="90"
+                android:startColor="@color/modern_grey_500"
+                android:endColor="@color/modern_grey_500" />
         </shape>
     </item>
 
-    <!-- @android:id/secondaryProgress can also be added, but is not necessary here. -->
-    <item android:id="@android:id/progress">
+    <item android:id="@android:id/progress"
+        android:gravity="center_vertical|fill_horizontal">
         <clip>
-            <shape android:shape="line">
-                <stroke
-                    android:color="@color/default_primary_color"
-                    android:width="@dimen/photo_picker_seek_bar_thickness" />
+            <shape android:shape="rectangle">
+                <corners android:radius="@dimen/photo_picker_seek_bar_edge_radius" />
+                <size android:height="@dimen/photo_picker_seek_bar_thickness" />
+                <gradient
+                    android:angle="90"
+                    android:startColor="@color/default_primary_color"
+                    android:endColor="@color/default_primary_color" />
             </shape>
         </clip>
     </item>

chrome/android/java/res/values/dimens.xml

@@ -438,6 +438,7 @@
     <dimen name="photo_picker_grainy_thumbnail_size">12dp</dimen>
     <dimen name="photo_picker_play_button_size">84dp</dimen>
     <dimen name="photo_picker_seek_bar_thickness">4dp</dimen>
+    <dimen name="photo_picker_seek_bar_edge_radius">2dp</dimen>
     <dimen name="photo_picker_seek_bar_thumb_size">12dp</dimen>
     <dimen name="photo_picker_video_duration_offset">16dp</dimen>