Bug 1338443 Part 2 - Convert nsAutoFloatManager::mNew to use UniquePtr. r=dholbert

The life cycle of nsFloatManager managed by mNew is same as
nsAutoFloatManager, which lives only in nsBlockFrame::Reflow(). Therefore,
other nsFloatManager pointers are all non-owning ref to the
nsAutoFloatManager::mNew.

MozReview-Commit-ID: B34BOcsjE2X

--HG--
extra : rebase_source : 49e4adaf31537b4003ee1a3db315f3e8bd8b1a7f

layout/generic/ReflowInput.h

@@ -337,7 +337,8 @@ struct ReflowInput : public SizeComputationInput {
   // parent's reflow state
   const ReflowInput* mParentReflowInput;
 
-  // pointer to the float manager associated with this area
+  // A non-owning pointer to the float manager associated with this area,
+  // which points to the object owned by nsAutoFloatManager::mNew.
   nsFloatManager* mFloatManager;
 
   // LineLayout object (only for inline reflow; set to nullptr otherwise)

layout/generic/nsFloatManager.cpp

@@ -979,28 +979,28 @@ nsAutoFloatManager::~nsAutoFloatManager()
       }
     }
 #endif
-
-    delete mNew;
   }
 }
 
 void
 nsAutoFloatManager::CreateFloatManager(nsPresContext *aPresContext)
 {
+  MOZ_ASSERT(!mNew, "Redundant call to CreateFloatManager!");
+
   // Create a new float manager and install it in the reflow
   // input. `Remember' the old float manager so we can restore it
   // later.
-  mNew = new nsFloatManager(aPresContext->PresShell(),
-                            mReflowInput.GetWritingMode());
+  mNew = MakeUnique<nsFloatManager>(aPresContext->PresShell(),
+                                    mReflowInput.GetWritingMode());
 
 #ifdef DEBUG
   if (nsBlockFrame::gNoisyFloatManager) {
     printf("constructed new float manager %p (replacing %p)\n",
-           mNew, mReflowInput.mFloatManager);
+           mNew.get(), mReflowInput.mFloatManager);
   }
 #endif
 
   // Set the float manager in the existing reflow input.
   mOld = mReflowInput.mFloatManager;
-  mReflowInput.mFloatManager = mNew;
+  mReflowInput.mFloatManager = mNew.get();
 }

layout/generic/nsFloatManager.h

@@ -549,9 +549,9 @@ class nsAutoFloatManager {
 
 public:
   explicit nsAutoFloatManager(ReflowInput& aReflowInput)
-    : mReflowInput(aReflowInput),
-      mNew(nullptr),
-      mOld(nullptr) {}
+    : mReflowInput(aReflowInput)
+    , mOld(nullptr)
+  {}
 
   ~nsAutoFloatManager();
 
@@ -565,8 +565,11 @@ public:
 
 protected:
   ReflowInput &mReflowInput;
-  nsFloatManager *mNew;
-  nsFloatManager *mOld;
+  mozilla::UniquePtr<nsFloatManager> mNew;
+
+ // A non-owning pointer, which points to the object owned by
+ // nsAutoFloatManager::mNew.
+  nsFloatManager* mOld;
 };
 
 #endif /* !defined(nsFloatManager_h_) */

layout/generic/nsLineLayout.h

@@ -381,7 +381,11 @@ public:
 
 protected:
   // This state is constant for a given block frame doing line layout
+
+  // A non-owning pointer, which points to the object owned by
+  // nsAutoFloatManager::mNew.
   nsFloatManager* mFloatManager;
+
   const nsStyleText* mStyleText; // for the block
   const ReflowInput* mBlockReflowInput;