Adding proper dragging behavior for L/R maximized windows.

ash/wm/workspace/frame_maximize_button.cc

Index: ash/wm/workspace/frame_maximize_button.cc
diff --git a/ash/wm/workspace/frame_maximize_button.cc b/ash/wm/workspace/frame_maximize_button.cc
index cf63df127a6576a51f41cf0015a8545a85ce770a..e04b7aa0d30345b367da133efa26640aaf6c88d4 100644
--- a/ash/wm/workspace/frame_maximize_button.cc
+++ b/ash/wm/workspace/frame_maximize_button.cc
@@ -551,9 +551,12 @@ MaximizeBubbleFrameState
   gfx::Rect screen = gfx::Screen::GetDisplayMatching(bounds).work_area();
   if (bounds.width() < (screen.width() * kMinSnapSizePercent) / 100)
     return FRAME_STATE_NONE;
+  // We might still have a horizontally filled window at this point which we
+  // treat as no special state.
+  if (bounds.y() != screen.y() || bounds.height() >= screen.height())
+    return FRAME_STATE_NONE;
+
   // We have to be in a maximize mode at this point.
-  DCHECK(bounds.y() == screen.y());
-  DCHECK(bounds.height() >= screen.height());
   if (bounds.x() == screen.x())
     return FRAME_STATE_SNAP_LEFT;
   if (bounds.right() == screen.right())