Open just folder menu on middle clicking chevron button.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm

Index: chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm
diff --git a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm
index 685c00b4fbba6ac07dbeb5646403cb7e904c5d0d..4ae686eab767f89a7d7302d598f4728e7ac60729 100644
--- a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm
+++ b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm
@@ -716,13 +716,29 @@ void RecordAppLaunch(Profile* profile, GURL url) {
     RecordBookmarkFolderOpen([self bookmarkLaunchLocation]);
   showFolderMenus_ = !showFolderMenus_;
 
-  if (sender == offTheSideButton_)
+  // Middle click on chevron should not open bookmarks under it, instead just
+  // open its folder menu.
+  if (sender == offTheSideButton_) {
     [[sender cell] setStartingChildIndex:displayedButtonCount_];
-
+    NSEvent* event = [NSApp currentEvent];
+    if ([event type] == NSOtherMouseUp) {
+      [self openFolderForOffTheSideButton:sender];
+      return;
+    }
+  }
   // Toggle presentation of bar folder menus.
   [folderTarget_ openBookmarkFolderFromButton:sender];
 }
 
+// Function to open bookmark folder of offTheSideButton.

[Alexei Svitkine (slow), 2014/09/19 15:49:59]

Nit: This comment doesn't add anything that the name of the function doesn't
say, so just omit.

[Gaja, 2014/09/20 05:35:44]

Acknowledged.

[Gaja, 2014/09/22 03:34:40]

Done.

+- (void)openFolderForOffTheSideButton:(id)sender {

[Alexei Svitkine (slow), 2014/09/19 15:49:59]

Nit: Since this can close it too, how about "openOrCloseFolder..."

[Gaja, 2014/09/20 05:35:44]

Acknowledged.

[Gaja, 2014/09/22 03:34:40]

Done.

+  // If clicked on already opened folder, then close it and return.
+  if ([folderController_ parentButton] == sender)

[Alexei Svitkine (slow), 2014/09/19 15:49:59]

From the code, looks like |sender| will always be |offTheSideButton_|, so I
don't think it's necessary to pass it as a param. Remove the param and change
this check to == offTheSideButton_ instead.

[Gaja, 2014/09/20 05:35:44]

Acknowledged.

[Gaja, 2014/09/22 03:34:40]

Done.

+    [self closeBookmarkFolder:self];
+  else
+    [self addNewFolderControllerWithParentButton:sender];
+}
+
 // Click on a bookmark folder button.
 - (IBAction)openBookmarkFolderFromButton:(id)sender {
   [self openBookmarkFolder:sender];