Bug 1239251 - Initialize mCommonAncestorWithLastFrame with nullptr in constructor BuildTextRunsScanner. r=roc

layout/generic/nsTextFrame.cpp

@@ -869,6 +869,7 @@ public:
     mCurrentFramesAllSameTextRun(nullptr),
     mDrawTarget(aDrawTarget),
     mLineContainer(aLineContainer),
+    mCommonAncestorWithLastFrame(nullptr),
     mMissingFonts(aPresContext->MissingFontRecorder()),
     mBidiEnabled(aPresContext->BidiEnabled()),
     mSkipIncompleteTextRuns(false),