To ensure that the location bar will not reach the minimum width.

chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm

Index: chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm
diff --git a/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm b/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm
index 0dd797acccc9715a371e6e0108d7bab92ad5500c..4d965109a967be983a643b7b46896d5a030b3c7a 100644
--- a/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm
+++ b/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm
@@ -89,6 +89,7 @@ const CGFloat kWrenchMenuLeftPadding = 3.0;
 - (void)pinLocationBarToLeftOfBrowserActionsContainerAndAnimate:(BOOL)animate;
 - (void)maintainMinimumLocationBarWidth;
 - (void)adjustBrowserActionsContainerForNewWindow:(NSNotification*)notification;
+- (void)browserActionsContainerWillDrag:(NSNotification*)notification;
 - (void)browserActionsContainerDragged:(NSNotification*)notification;
 - (void)browserActionsContainerDragFinished:(NSNotification*)notification;
 - (void)browserActionsVisibilityChanged:(NSNotification*)notification;
@@ -587,6 +588,11 @@ class NotificationBridge : public WrenchMenuBadgeController::Delegate {
               containerView:browserActionsContainerView_]);
     [[NSNotificationCenter defaultCenter]
         addObserver:self
+           selector:@selector(browserActionsContainerWillDrag:)
+               name:kBrowseActionContainerWillTranslateOnXNotification

[Yoyo Zhou, 2014/10/27 23:45:26]

typo: kBrowserAction...

[Malcolm, 2014/10/28 06:56:09]

Oops, I lost the 'r'.
On 2014/10/27 23:45:26, Yoyo Zhou wrote:

+             object:browserActionsController_];
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
            selector:@selector(browserActionsContainerDragged:)
                name:kBrowserActionGrippyDraggingNotification
              object:browserActionsController_];
@@ -635,6 +641,18 @@ class NotificationBridge : public WrenchMenuBadgeController::Delegate {
   [self pinLocationBarToLeftOfBrowserActionsContainerAndAnimate:YES];
 }
 
+- (void)browserActionsContainerWillDrag:(NSNotification*)notification {
+  CGFloat deltaX = [[notification.userInfo objectForKey:kTranslationWithDelta]
+      floatValue];
+  CGFloat locationBarWidth = NSWidth([locationBar_ frame]);

[Yoyo Zhou, 2014/10/27 23:45:26]

I'm not very familiar with this code, so please bear with me. Is there some
reason we can't use maintainMinimumLocationBarWidth?

[Malcolm, 2014/10/28 06:56:09]

The -maintainMinimumLocationBarWidth only adjusts the location bar to guarantee
the minimum size of it, not the frame of browserActionsContainerView. So if we
just call -maintainMinimumLocationBarWidth, the browserActionsContainerView will
still overlap the locationbar, although the locationbar will be minimum size.
Actually, the frame of browserActionsContainerView is changed in the internal of
it (-mouseDragged:). By setting the property "canDragLeft" here can tell the
browserActionsContainerView that whether the dragging is allowed in
-mouseDragged:. If not, the -setFrame will not executed in -mouseDragged: of
browserActionsContainerView.
On 2014/10/27 23:45:26, Yoyo Zhou wrote:

+  BOOL locationBarWillBeAtMinSize =
+      (locationBarWidth + deltaX) <= kMinimumLocationBarWidth;
+
+  // Prevent the |browserActionsContainerView_| from dragging if the width of
+  // location bar will reach the minimum.
+  [browserActionsContainerView_ setCanDragLeft:!locationBarWillBeAtMinSize];
+}
+
 - (void)browserActionsVisibilityChanged:(NSNotification*)notification {
   [self pinLocationBarToLeftOfBrowserActionsContainerAndAnimate:NO];
 }