Implement the new Photo picker, part two.

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

+<?xml version="1.0" encoding="utf-8"?>

[Theresa, 2017/03/21 15:36:59]

This needs a copyright comment.

[Finnur, 2017/03/27 16:50:41]

Done.

+<shape xmlns:android="http://schemas.android.com/apk/res/android">
+    <gradient
+        android:startColor="#42000000"

[Theresa, 2017/03/21 15:36:59]

Please define this in colors.xml. We have a TON of colors already, so ideally,
if this is close enough to a color that's already used somewhere in Chrome we
should use that. If it's not close enough to an existing color, the alpha %
should be a value that's likely to be reused (e.g.  40000000 would be 25% or
4D000000 would be 30%).

[Finnur, 2017/03/27 16:50:41]

Done.

+        android:endColor="#00000000"

[Theresa, 2017/03/21 15:36:59]

nit: @android:color/black

[Finnur, 2017/03/27 16:50:41]

Done.

+        android:type="radial"
+        android:gradientRadius="64dp"
+        android:centerY="0%"
+        android:centerX="0%" />
+</shape>