Bug 881018 - Crash when TiledLayerBuffer::GetScaledTileLength returns 0; r=cwiiis

gfx/layers/TiledLayerBuffer.h

@@ -111,7 +111,16 @@ public:
   bool RemoveTile(int x, int y, Tile& aRemovedTile);
 
   uint16_t GetTileLength() const { return TILEDLAYERBUFFER_TILE_SIZE; }
-  uint32_t GetScaledTileLength() const { return TILEDLAYERBUFFER_TILE_SIZE / mResolution; }
+  uint32_t GetScaledTileLength() const {
+    // volatile variables to help investigate bug 881018
+    volatile float resolution = mResolution;
+    volatile float fScaledLength = TILEDLAYERBUFFER_TILE_SIZE / mResolution;
+    volatile uint32_t uiScaledLength = TILEDLAYERBUFFER_TILE_SIZE / mResolution;
+    if (!uiScaledLength) {
+        MOZ_CRASH();
+    }
+    return uiScaledLength;
+  }
 
   unsigned int GetTileCount() const { return mRetainedTiles.Length(); }