Bug 836565, Part 2: Perform a horizontal resize reflow instead of a full reflow when reflowing on zoom to get better performance. [r=dbaron]

layout/base/nsIPresShell.h

@@ -1391,6 +1391,26 @@ public:
 
   void SetMaxLineBoxWidth(nscoord aMaxLineBoxWidth);
 
+  /**
+   * Returns whether or not there is a reflow on zoom event pending. A reflow
+   * on zoom event is a change to the max line box width, followed by a reflow.
+   * This subsequent reflow event should treat all frames as though they resized
+   * horizontally (and thus reflow all their descendants), rather than marking
+   * all frames dirty from the root. This is the way the pres shell indicates
+   * that an hresize reflow should take place during reflow state construction.
+   */
+  bool IsReflowOnZoomPending() {
+    return mReflowOnZoomPending;
+  }
+
+  /**
+   * Clear the flag indicating whether a reflow on zoom event is pending. This
+   * is performed at the very end of DoReflow().
+   */
+  void ClearReflowOnZoomPending() {
+    mReflowOnZoomPending = false;
+  }
+
 protected:
   friend class nsRefreshDriver;
 
@@ -1499,6 +1519,10 @@ protected:
   bool mFontSizeInflationForceEnabled;
   bool mFontSizeInflationDisabledInMasterProcess;
 
+  // Flag to indicate whether or not there is a reflow on zoom event pending.
+  // See IsReflowOnZoomPending() for more information.
+  bool mReflowOnZoomPending;
+
   // The maximum width of a line box. Text on a single line that exceeds this
   // width will be wrapped. A value of 0 indicates that no limit is enforced.
   nscoord mMaxLineBoxWidth;

layout/base/nsPresShell.cpp

@@ -1877,7 +1877,7 @@ PresShell::ResizeReflowIgnoreOverride(nscoord aWidth, nscoord aHeight)
         DoReflow(rootFrame, true);
       }
 
-      DidDoReflow(true);
+      DidDoReflow(true, false);
     }
   }
 
@@ -7627,7 +7627,7 @@ PresShell::WillDoReflow()
 }
 
 void
-PresShell::DidDoReflow(bool aInterruptible)
+PresShell::DidDoReflow(bool aInterruptible, bool aWasInterrupted)
 {
   mFrameConstructor->EndUpdate();
   
@@ -7641,6 +7641,10 @@ PresShell::DidDoReflow(bool aInterruptible)
     mCaret->InvalidateOutsideCaret();
     mCaret->UpdateCaretPosition();
   }
+
+  if (!aWasInterrupted) {
+    ClearReflowOnZoomPending();
+  }
 }
 
 static PLDHashOperator
@@ -7933,7 +7937,7 @@ PresShell::ProcessReflowCommands(bool aInterruptible)
 
     // Exiting the scriptblocker might have killed us
     if (!mIsDestroying) {
-      DidDoReflow(aInterruptible);
+      DidDoReflow(aInterruptible, interrupted);
     }
 
     // DidDoReflow might have killed us
@@ -9476,6 +9480,7 @@ nsIPresShell::SetMaxLineBoxWidth(nscoord aMaxLineBoxWidth)
 
   if (mMaxLineBoxWidth != aMaxLineBoxWidth) {
     mMaxLineBoxWidth = aMaxLineBoxWidth;
-    FrameNeedsReflow(GetRootFrame(), eResize, NS_FRAME_IS_DIRTY);
+    mReflowOnZoomPending = true;
+    FrameNeedsReflow(GetRootFrame(), eResize, NS_FRAME_HAS_DIRTY_CHILDREN);
   }
 }

layout/base/nsPresShell.h

@@ -359,7 +359,15 @@ protected:
                           bool aTouchIsNew);
 
   void     WillDoReflow();
-  void     DidDoReflow(bool aInterruptible);
+
+  /**
+   * Callback handler for whether reflow happened.
+   *
+   * @param aInterruptible Whether or not reflow interruption is allowed.
+   * @param aWasInterrupted Whether or not the reflow was interrupted earlier.
+   *
+   */
+  void     DidDoReflow(bool aInterruptible, bool aWasInterrupted);
   // ProcessReflowCommands returns whether we processed all our dirty roots
   // without interruptions.
   bool     ProcessReflowCommands(bool aInterruptible);

layout/generic/nsHTMLReflowState.cpp

@@ -424,8 +424,9 @@ IsQuirkContainingBlockHeight(const nsHTMLReflowState* rs, nsIAtom* aFrameType)
 void
 nsHTMLReflowState::InitResizeFlags(nsPresContext* aPresContext, nsIAtom* aFrameType)
 {
-  bool isHResize = frame->GetSize().width !=
-                     mComputedWidth + mComputedBorderPadding.LeftRight();
+  bool isHResize = (frame->GetSize().width !=
+                     mComputedWidth + mComputedBorderPadding.LeftRight()) ||
+                     aPresContext->PresShell()->IsReflowOnZoomPending();
 
   if ((frame->GetStateBits() & NS_FRAME_FONT_INFLATION_FLOW_ROOT) &&
       nsLayoutUtils::FontSizeInflationEnabled(aPresContext)) {