Bug 138057. Eliminate nsBlockFrame::RememberFloaterDamage, instead

recording the damage when we reflow the floater. This allows us to
catch several cases that we weren't catching before, so we no longer
need to dirty all the line boxes when an incremental reflow targeted
at a float arrives. r=dbaron, sr=attinasi.

layout/doc/HLD-SpaceManager.html

@@ -54,20 +54,22 @@ the space  taken up by floaters (UpdateSpaceManager in nsBlockFrame) and
 provides information  about the space available for other elements (GetAvailableSpace
 in nsBlockReflowState).  &nbsp;<br>
  <br>
- Additionally, there is a need to manage impacts to lines caused by changes 
-to floated elements. &nbsp;This is referred to as Propagation of Floater Damage
-and is handled by the Block Frame, making use of teh Space Manager. When
-dirty lines are incrementally reflowed, the Space Manger is told about the
-larger of the new or old line combined width, which it records in an internal
-nsIntervalSet as potential floater damage (the method is IncludeInDamage). 
-During the incremental reflow of dirty lines the block frame may encounter 
-lines that are NOT dirty. In this case the Space Manager is also asked if 
-&nbsp;there is any floater damage, and if there is then the block further 
-checks to see if that damage intersects the area of the non-dirty line, marking 
-it dirty if there is intersection. &nbsp;Thus, changes to floaters on other 
-lines may cause impact to otherwise clean lines, and the Space Manager facilitates 
-the detection of this.  
-<h2>Data Model</h2>
+ Additionally, there is a need to manage impacts to lines caused by
+changes to floated elements. &nbsp;This is referred to as Propagation
+of Floater Damage and is handled by the Block Frame, making use of the
+Space Manager. When a float is incrementally reflowed, the Space
+Manger is notified if the floater's region has changed. If so, the
+vertical space that has been affected (including both the float's old
+region and the float's new region) is noted in the internal
+nsIntervalSet as potential floater damage (the method is
+IncludeInDamage).  During the incremental reflow of dirty lines the
+block frame may encounter lines that are NOT dirty. In this case the
+Space Manager is also asked if &nbsp;there is any floater damage, and
+if there is then the block further checks to see if that damage
+intersects the area of the non-dirty line, marking it dirty if there
+is intersection. &nbsp;Thus, changes to floaters on other lines may
+cause impact to otherwise clean lines, and the Space Manager
+facilitates the detection of this.  <h2>Data Model</h2>
  
 <h4>Class/Component Diagram</h4>
  
@@ -150,6 +152,7 @@ origin.&nbsp;       <br>
 
 The general algorightm in <i>nsBlockReflowState::FlowAndPlaceFloater</i> is:<br>
 <ul>
+  <li>The region that the float currently occupies is recorded.</li>
   <li>The band of available space is searched (with nsBlockReflowState::GetAvailableSpace);</li>
   <li>The floater frame that is get from the passed nsFloaterCache argument is reflowed
   and its rect is retriven with GetRect;</li>
@@ -160,6 +163,8 @@ The general algorightm in <i>nsBlockReflowState::FlowAndPlaceFloater</i> is:<br>
       <a href="http://www.w3.org/TR/REC-CSS2/visuren.html#float-position">CSS2/9.5.1/4</a>
       is not respected;</li>
   <li>Add the floater using <i>nsSpaceManager::AddRectRegion</i> </li>
+  <li>Compare the area that the float used to occupy with the area that it now occupies: if different,
+      record the vertically affected interval using <i>nsSpaceManager::IncludeInDamage</i></li>
 </ul>
   <h4>Use Case 3: Space Manager is used to find available space to reflow
  into</h4>
@@ -188,17 +193,7 @@ and determines the right-most edge of the available space.</li>
    
   </ul>
    
-  <h4>Use Case 4: Propagation of Floater Damage: remembering floater damage</h4>
- This process is driven by the Block Frame.<br>
-   
-  <ul>
-     <li>A dirty line is reflowed</li>
-     <li>If the line's combined area has changed then the Space Manager is 
-told to include the combined area as a floater damage interval.</li>
-   
-  </ul>
-   
-  <h4>Use Case 5: Propagation of Floater Damage: detecting and handling floater 
+  <h4>Use Case 4: Propagation of Floater Damage: detecting and handling floater 
 damage</h4>
   This process is driven by the Block Frame.<br>