[ProfilePicker]: Add scrollbar to the profile container grid.

Screenshot: https://drive.google.com/file/d/1TVPFiVBhgMFsdfOHSL9AvrJqF_cHKFBC/view?usp=sharing

Bug: 1063856
Change-Id: Ibaa987e941d11269eacfe1dc091dab234f8b206e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2302034Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Monica Basta <msalama@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789879}

chrome/browser/resources/signin/profile_picker/profile_picker_app.html

@@ -3,7 +3,6 @@
     display: flex;
     font-size: 100%;
     margin: 0;
-    min-height: 100vh;
   }
 </style>
 <cr-view-manager id="viewManager">

chrome/browser/resources/signin/profile_picker/profile_picker_main_view.html

@@ -30,6 +30,7 @@
     --grid-gutter: 24px;
     --profile-item-height:178px;
     --profile-item-width: 162px;
+    --scrollbar-width: 4px;
     align-items: center;
     display: grid;
     grid-column-gap: var(--grid-gutter);
@@ -39,6 +40,26 @@
     margin: auto;
     margin-inline-end: 140px;
     margin-inline-start: 140px;
+    max-height: calc((var(--profile-item-height) + var(--grid-gutter)) * 2 +
+        30px);
+    overflow-y: auto;
+    padding-inline-end: var(--scrollbar-width);
+    padding-inline-start: var(--scrollbar-width);
+  }
+
+  .profiles-container::-webkit-scrollbar {
+    width: var(--scrollbar-width);
+  }
+
+  /* Track */
+  .profiles-container::-webkit-scrollbar-track {
+    border-radius: var(--scrollbar-width);
+  }
+
+  /* Handle */
+  .profiles-container::-webkit-scrollbar-thumb {
+    background: var(--google-grey-refresh-100);
+    border-radius: var(--scrollbar-width);
   }
 
   .profile-item {
@@ -60,8 +81,8 @@
     --cr-icon-button-icon-size: var(--avatar-icon-size);
     --cr-icon-button-size: 84px;
     --cr-icon-button-fill-color: var(--google-grey-refresh-100);
-  --cr-icon-button-margin-end: 0px;
-  --cr-icon-button-margin-start: 0px;
+    --cr-icon-button-margin-end: 0;
+    --cr-icon-button-margin-start: 0;
     --cr-icon-button-stroke-color: var(--google-grey-refresh-700);
   }