b=385584, crash with toDataURL on large canvas, r=stuart

content/canvas/src/nsCanvasRenderingContext2D.cpp

@@ -720,6 +720,14 @@ nsCanvasRenderingContext2D::Render(nsIRenderingContext *rc)
 {
     nsresult rv = NS_OK;
 
+    if (!mSurface || !mCairo ||
+        cairo_surface_status(mSurface) != CAIRO_STATUS_SUCCESS ||
+        cairo_status(mCairo) != CAIRO_STATUS_SUCCESS)
+        return NS_ERROR_FAILURE;
+
+    if (!mThebesSurface)
+        return NS_ERROR_FAILURE;
+
     gfxContext* ctx = (gfxContext*) rc->GetNativeGraphicData(nsIRenderingContext::NATIVE_THEBES_CONTEXT);
     nsRefPtr<gfxPattern> pat = new gfxPattern(mThebesSurface);
 
@@ -748,14 +756,12 @@ nsCanvasRenderingContext2D::GetInputStream(const nsACString& aMimeType,
                                            const nsAString& aEncoderOptions,
                                            nsIInputStream **aStream)
 {
+    if (!mSurface || cairo_surface_status(mSurface) != CAIRO_STATUS_SUCCESS)
+        return NS_ERROR_FAILURE;
+
     nsCString conid(NS_LITERAL_CSTRING("@mozilla.org/image/encoder;2?type="));
     conid += aMimeType;
 
-    if (cairo_status(mCairo)) {
-        fprintf (stderr, "Cairo error! %d %s\n", cairo_status(mCairo), cairo_status_to_string(cairo_status(mCairo)));
-        fflush (stderr);
-    }
-
     nsCOMPtr<imgIEncoder> encoder = do_CreateInstance(conid.get());
     if (!encoder)
         return NS_ERROR_FAILURE;

content/html/content/src/nsHTMLCanvasElement.cpp

@@ -455,10 +455,16 @@ nsHTMLCanvasElement::GetContext(const nsAString& aContextId,
       return NS_ERROR_INVALID_ARG;
 
     rv = mCurrentContext->SetCanvasElement(this);
-    NS_ENSURE_SUCCESS(rv, rv);
+    if (NS_FAILED(rv)) {
+      mCurrentContext = nsnull;
+      return rv;
+    }
 
     rv = UpdateContext();
-    NS_ENSURE_SUCCESS(rv, rv);
+    if (NS_FAILED(rv)) {
+      mCurrentContext = nsnull;
+      return rv;
+    }
 
     mCurrentContextId.Assign(aContextId);
   } else if (!mCurrentContextId.Equals(aContextId)) {