Back out bug 305705 to test performance impact.

layout/forms/nsComboboxControlFrame.cpp

@@ -1555,30 +1555,28 @@ nsComboboxControlFrame::Reflow(nsPresContext*          aPresContext,
                      mDisplayFrame, mButtonFrame, mItemDisplayWidth, scrollbarWidth, 
                      aReflowState.mComputedBorderPadding, size.height);
 
-  // The dropdown was reflowed UNCONSTRAINED before, now we need to reflow it
-  // so that all children match the desired width.
-  // The dropdown MUST always be either the same size as the combo or larger
-  // if necessary. Note that individual children can be narrower in case they
-  // are constrained by 'width', 'max-width' etc.
-  if (eReflowReason_Initial == firstPassState.reason) {
-    firstPassState.reason = eReflowReason_Resize;
-  }
-  REFLOW_DEBUG_MSG3("*** Reflowing ListBox to width: %d it was %d\n", PX(aDesiredSize.width), PX(dropdownDesiredSize.width));
+  // The dropdown was reflowed UNCONSTRAINED before, now we need to check to see
+  // if it needs to be resized. 
+  //
+  // Optimization - The style (font, etc.) maybe different for the display item 
+  // than for any particular item in the dropdown. So, if the new size of combobox
+  // is smaller than the dropdown, that is OK, The dropdown MUST always be either the same
+  // size as the combo or larger if necessary
+  if (aDesiredSize.width > dropdownDesiredSize.width) {
+    if (eReflowReason_Initial == firstPassState.reason) {
+      firstPassState.reason = eReflowReason_Resize;
+    }
+    REFLOW_DEBUG_MSG3("*** Reflowing ListBox to width: %d it was %d\n", PX(aDesiredSize.width), PX(dropdownDesiredSize.width));
 
-  // Tell it we are doing the second pass, which means we will skip
-  // doing the unconstained reflow, we already know that size
-  nsListControlFrame * lcf = NS_STATIC_CAST(nsListControlFrame*, mDropdownFrame);
-  lcf->SetPassId(2);
-  // Reflow the dropdown list to be
-  // MAX(width of the display + button, width of the widest option). bug 305705.
-  const nscoord availableWidth =
-    PR_MAX(aDesiredSize.width, dropdownDesiredSize.width -
-                               aReflowState.mComputedBorderPadding.left -
-                               aReflowState.mComputedBorderPadding.right);
-  ReflowComboChildFrame(mDropdownFrame, aPresContext, dropdownDesiredSize,
-                        firstPassState, aStatus,
-                        availableWidth, NS_UNCONSTRAINEDSIZE);
-  lcf->SetPassId(0);
+    // Tell it we are doing the second pass, which means we will skip
+    // doing the unconstained reflow, we already know that size
+    nsListControlFrame * lcf = NS_STATIC_CAST(nsListControlFrame*, mDropdownFrame);
+    lcf->SetPassId(2);
+    // Reflow the dropdown list to match the width of the display + button
+    ReflowComboChildFrame(mDropdownFrame, aPresContext, dropdownDesiredSize, firstPassState, aStatus, 
+                          aDesiredSize.width, NS_UNCONSTRAINEDSIZE);
+    lcf->SetPassId(0);
+  }
 
   // Set the max element size to be the same as the desired element size.
   if (aDesiredSize.mComputeMEW) {