Bug 1142975 - Check for Present()-caused context loss. - r=kamidphish

dom/canvas/WebGLContext.cpp

@@ -749,6 +749,8 @@ bool
 WebGLContext::ResizeBackbuffer(uint32_t requestedWidth,
                                uint32_t requestedHeight)
 {
+    MOZ_ASSERT(!IsContextLost());
+
     uint32_t width = requestedWidth;
     uint32_t height = requestedHeight;
 
@@ -827,6 +829,11 @@ WebGLContext::SetDimensions(int32_t signedWidth, int32_t signedHeight)
         // If we've already drawn, we should commit the current buffer.
         PresentScreenBuffer();
 
+        if (IsContextLost()) {
+            GenerateWarning("WebGL context was lost due to swap failure.");
+            return NS_OK;
+        }
+
         // ResizeOffscreen scraps the current prod buffer before making a new one.
         if (!ResizeBackbuffer(width, height)) {
             GenerateWarning("WebGL context failed to resize.");