Adds some debugging code in hopes of isolating a crasher. From the...

chrome/browser/views/tabs/tab_strip.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/views/tabs/tab_strip.h"
 
 #include "app/drag_drop_types.h"
 #include "app/gfx/canvas.h"
 #include "app/gfx/path.h"
 #include "app/l10n_util.h"
@@ skipping 1174 matching lines @@
     GetTabAt(i)->StopPulse();
 }
 
 void TabStrip::MaybeStartDrag(Tab* tab, const views::MouseEvent& event) {
   // Don't accidentally start any drag operations during animations if the
   // mouse is down... during an animation tabs are being resized automatically,
   // so the View system can misinterpret this easily if the mouse is down that
   // the user is dragging.
   if (IsAnimating() || tab->closing() || !HasAvailableDragActions())
     return;
+  int index = GetIndexOfTab(tab);
+  if (!model_->ContainsIndex(index)) {
+    // It appears to be possible for a drag to start with an invalid tab.
+    // This records some extra information in hopes of tracking down why.
+    // The string contains the following, in order:
+    // . If a drag is already in progress, a 'D'.
+    // . Index of tab the user is dragging.
+    // . Number of tabs.
+    // . Size of the model.
+    // . Indices of any tabs that are being closed.
+    // . ! end marker.
+    std::string tmp;
+    if (drag_controller_.get())
+      tmp += "D";
+    tmp += " " + IntToString(index);
+    tmp += " " + IntToString(GetTabCount());
+    tmp += " " + IntToString(model_->count());
+    for (int i = 0; i < GetTabCount(); ++i) {
+      if (GetTabAt(i)->closing())
+        tmp += " " + IntToString(i);
+    }
+    tmp += "!";  // End marker so we know we got all closing tabs.
+
+    volatile char tab_state[128];
+    for (size_t i = 0; i < std::min(ARRAYSIZE_UNSAFE(tab_state),
+                                    tmp.size()); ++i) {
+      tab_state[i] = tmp[i];
+    }
+    CHECK(false);
+    return;
+  }
   drag_controller_.reset(new DraggedTabController(tab, this));
   drag_controller_->CaptureDragInfo(gfx::Point(event.x(), event.y()));
 }
 
 void TabStrip::ContinueDrag(const views::MouseEvent& event) {
   // We can get called even if |MaybeStartDrag| wasn't called in the event of
   // a TabStrip animation when the mouse button is down. In this case we should
   // _not_ continue the drag because it can lead to weird bugs.
   if (drag_controller_.get())
     drag_controller_->Drag();
@@ skipping 744 matching lines @@
               &TabStrip::ResizeLayoutTabs),
           kResizeTabsTimeMs);
     }
   } else {
     // Mouse moved quickly out of the tab strip and then into it again, so
     // cancel the timer so that the strip doesn't move when the mouse moves
     // back over it.
     resize_layout_factory_.RevokeAll();
   }
 }