Bug 1313381 - Add assertions to nsDeviceContext to assert that it is only initialized once. r=mstange

--HG--
extra : rebase_source : b6ccdd30e7443012b4fc061814a7243807663920

gfx/src/nsDeviceContext.cpp

@@ -194,6 +194,9 @@ nsDeviceContext::nsDeviceContext()
       mAppUnitsPerDevPixel(-1), mAppUnitsPerDevPixelAtUnitFullZoom(-1),
       mAppUnitsPerPhysicalInch(-1),
       mFullZoom(1.0f), mPrintingScale(1.0f)
+#ifdef DEBUG
+    , mIsInitialized(false)
+#endif
 {
     MOZ_ASSERT(NS_IsMainThread(), "nsDeviceContext created off main thread");
 }
@@ -299,6 +302,13 @@ nsDeviceContext::SetDPI(double* aScale)
 nsresult
 nsDeviceContext::Init(nsIWidget *aWidget)
 {
+#ifdef DEBUG
+    // We can't assert |!mIsInitialized| here since EndSwapDocShellsForDocument
+    // re-initializes nsDeviceContext objects.  We can only assert in
+    // InitForPrinting (below).
+    mIsInitialized = true;
+#endif
+
     nsresult rv = NS_OK;
     if (mScreenManager && mWidget == aWidget)
         return rv;
@@ -438,13 +448,18 @@ nsDeviceContext::InitForPrinting(nsIDeviceContextSpec *aDevice)
 {
     NS_ENSURE_ARG_POINTER(aDevice);
 
-    mDeviceContextSpec = aDevice;
+    MOZ_ASSERT(!mIsInitialized,
+               "Only initialize once, immediately after construction");
+
+    // We don't set mIsInitialized here. The Init() call below does that.
 
     mPrintTarget = aDevice->MakePrintTarget();
     if (!mPrintTarget) {
         return NS_ERROR_FAILURE;
     }
 
+    mDeviceContextSpec = aDevice;
+
     Init(nullptr);
 
     if (!CalcPrintingSize()) {

gfx/src/nsDeviceContext.h

@@ -288,6 +288,9 @@ private:
 #ifdef XP_MACOSX
     RefPtr<PrintTarget>            mCachedPrintTarget;
 #endif
+#ifdef DEBUG
+    bool mIsInitialized;
+#endif
 };
 
 #endif /* _NS_DEVICECONTEXT_H_ */