Mac Picker UI: Screen Auto Selection

chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm

Index: chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm
diff --git a/chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm b/chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm
index e2858cdd61e6293af69d41a920ae64b9e74b018f..b0c130c2c3c59d96d38efb797a38566dcadf880e 100644
--- a/chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm
+++ b/chrome/browser/ui/cocoa/media_picker/desktop_media_picker_controller.mm
@@ -597,7 +597,10 @@ NSString* const kTitleId = @"title";
 - (id)imageBrowser:(IKImageBrowserView*)browser itemAtIndex:(NSUInteger)index {
   DesktopMediaID::Type sourceType = [self sourceTypeForBrowser:browser];
   NSMutableArray* items = [self itemSetForType:sourceType];
-  return [items objectAtIndex:index];
+  id item = [items objectAtIndex:index];

[tapted, 2016/07/22 03:43:36]

id -> DesktopMediaPickerItem* (it's usually best to avoid duck-typing with `id`
when possible)

[qiangchen, 2016/07/22 18:33:54]

Done.

+  [item setTitleHidden:browser == screenBrowser_ && [items count] == 1];

[tapted, 2016/07/22 03:43:36]

this should have a comment - it's pretty subtle

[qiangchen, 2016/07/22 18:33:54]

Done.

+
+  return item;
 }
 
 #pragma mark IKImageBrowserDelegate
@@ -681,10 +684,17 @@ NSString* const kTitleId = @"title";
       [[DesktopMediaPickerItem alloc] initWithSourceId:source.id
                                               imageUID:++lastImageUID_
                                             imageTitle:imageTitle]);
+
   [items insertObject:item atIndex:index];
   [browser reloadData];
-  if (sourceType == DesktopMediaID::TYPE_WEB_CONTENTS)
+  if (sourceType == DesktopMediaID::TYPE_WEB_CONTENTS) {
+    // Memorizing selection.
     [self setTabBrowserIndex:selectedIndex];
+  } else if (sourceType == DesktopMediaID::TYPE_SCREEN && [items count] == 1) {
+    // Preselect the first screen source.
+    [browser setSelectionIndexes:[NSIndexSet indexSetWithIndex:0]
+            byExtendingSelection:NO];
+  }
 
   NSString* autoselectSource = base::SysUTF8ToNSString(
       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(