Bug 1304632 - Part 2: Remove unnecessary nsStyleImage::mImage null checking. r=bholley

nsStyleImage::mImage is always set to a non-null object when its mType
is eStyleImageType_Image, so let's just assert that and stop null
checking in that case.

MozReview-Commit-ID: 2ect4coV0LV

--HG--
extra : rebase_source : 768b0c5989bc3e32d4d8ab803d85885f223bcb43

layout/style/nsStyleStruct.cpp

@@ -2195,7 +2195,7 @@ nsStyleImage::ComputeActualCropRect(nsIntRect& aActualCropRect,
 nsresult
 nsStyleImage::StartDecoding() const
 {
-  if ((mType == eStyleImageType_Image) && mImage) {
+  if (mType == eStyleImageType_Image) {
     return mImage->StartDecoding();
   }
   return NS_OK;

layout/style/nsStyleStruct.h

@@ -365,6 +365,7 @@ struct nsStyleImage
   }
   imgRequestProxy* GetImageData() const {
     MOZ_ASSERT(mType == eStyleImageType_Image, "Data is not an image!");
+    MOZ_ASSERT(mImage);
     MOZ_ASSERT(mImageTracked,
                "Should be tracking any image we're going to use!");
     return mImage;