Bug 1239259 - Fix WebGL2 generateMipmap checking. r=jgilbert

--HG--
extra : rebase_source : 7bc5579f227ee5c21e2019aec53ac225e4e2dca9

dom/canvas/WebGLTexture.cpp

@@ -742,6 +742,12 @@ WebGLTexture::GenerateMipmap(TexTarget texTarget)
         return;
     }
 
+    if (!baseImageInfo.mFormat->isRenderable || !baseImageInfo.mFormat->isFilterable) {
+        mContext->ErrorInvalidOperation("generateMipmap: Texture at base level is not"
+                                        " color-renderable or texture-filterable.");
+        return;
+    }
+
     // Done with validation. Do the operation.
 
     mContext->MakeContextCurrent();