Fix unit test and check cancellation

src/Compilers/Core/CodeAnalysisTest/Diagnostics/OperationTests.cs

@@ -299,7 +299,7 @@ void M(int x)
             }
             catch (ArgumentNullException ex)
             {
-                Assert.Equal(ex, new ArgumentNullException("node"));
+                Assert.Equal(ex.Message, new ArgumentNullException("node").Message);
             }
 
             try
@@ -308,7 +308,7 @@ void M(int x)
             }
             catch (ArgumentNullException ex)
             {
-                Assert.Equal(ex, new ArgumentNullException("semanticModel"));
+                Assert.Equal(ex.Message, new ArgumentNullException("semanticModel").Message);
             }
 
             // Verify identical CFG from method body syntax and operation. 

src/Compilers/Core/Portable/Operations/ControlFlowGraph.cs

@@ -81,6 +81,7 @@ public static ControlFlowGraph Create(SyntaxNode node, SemanticModel semanticMod
             }
 
             IOperation operation = semanticModel.GetOperation(node, cancellationToken);
+            cancellationToken.ThrowIfCancellationRequested();
             return operation == null ? null : CreateCore(operation, nameof(operation));
         }