Update EoC thumbnail placeholder to modern grey 100

And create a generic thumbnail_placeholder_on_white_bg color for use in
Zine as well.

BUG=900757

Change-Id: I8cee89a7bfc361288b4f5b0041efb6dc2d8785c7
Reviewed-on: https://chromium-review.googlesource.com/c/1336062Reviewed-by: Becky Zhou <huayinz@chromium.org>
Commit-Queue: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608192}

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

@@ -5,7 +5,7 @@
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
     <solid
-        android:color="@color/placeholder_thumbnail_bg_color" />
+        android:color="@color/thumbnail_placeholder_on_white_bg" />
     <corners
         android:radius="@dimen/snippets_thumbnail_small_corner_radius" />
 </shape>
\ No newline at end of file

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

@@ -198,7 +198,7 @@
     <color name="bottom_system_nav_color">@android:color/white</color>
     <color name="bottom_system_nav_divider_color">@color/black_alpha_12</color>
     <color name="search_box_hint">@color/default_text_color_secondary</color>
-    <color name="placeholder_thumbnail_bg_color">#DADCE0</color>
+    <color name="thumbnail_placeholder_on_white_bg">@color/modern_grey_100</color>
     <color name="clear_browsing_data_selected_tab_color">@color/modern_blue_600</color>
 
 </resources>

chrome/android/java/src/org/chromium/chrome/browser/suggestions/SuggestionsBinder.java

@@ -238,7 +238,7 @@ public class SuggestionsBinder {
                     new ColorDrawable(mSuggestion.getThumbnailDominantColor() != null
                                     ? mSuggestion.getThumbnailDominantColor()
                                     : ApiCompatibilityUtils.getColor(mThumbnailView.getResources(),
-                                              R.color.modern_grey_100));
+                                              R.color.thumbnail_placeholder_on_white_bg));
             mThumbnailView.setImageDrawable(colorDrawable);
         } else {
             mThumbnailView.setImageResource(R.drawable.ic_snippet_thumbnail_placeholder);