Revert of Revert r403630 which broke parsing on some sites.

third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h

Index: third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h b/third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h
index 3b0f3749eec13250c6ae6615e4225b9c4b606c50..1d4d898b03dffd9cfa45d9777589daa763e7976e 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h
+++ b/third_party/WebKit/Source/core/html/parser/HTMLTreeBuilderSimulator.h
@@ -26,6 +26,7 @@
 #ifndef HTMLTreeBuilderSimulator_h
 #define HTMLTreeBuilderSimulator_h
 
+#include "core/CoreExport.h"
 #include "core/html/parser/HTMLParserOptions.h"
 #include "wtf/Vector.h"
 
@@ -35,13 +36,23 @@
 class HTMLTokenizer;
 class HTMLTreeBuilder;
 
-class HTMLTreeBuilderSimulator {
+class CORE_EXPORT HTMLTreeBuilderSimulator {
     USING_FAST_MALLOC(HTMLTreeBuilderSimulator);
 private:
     enum Namespace {
         HTML,
         SVG,
         MathML
+    };
+
+    struct StateFlags {
+        unsigned ns : 2; // Namespace
+        unsigned isHTMLIntegrationPoint : 1;
+
+        bool operator==(const StateFlags& other) const
+        {
+            return ns == other.ns && isHTMLIntegrationPoint == other.isHTMLIntegrationPoint;
+        }
     };
 
 public:
@@ -51,24 +62,35 @@
         OtherToken
     };
 
-    typedef Vector<Namespace, 1> State;
+    // The state of the tree builder simulator is an abbreviated stack
+    // of open elements that only contains entries for namespace
+    // changes, or elements which may change whether the current node
+    // is a HTML integration point.
+    typedef Vector<StateFlags, 1> State;
 
     explicit HTMLTreeBuilderSimulator(const HTMLParserOptions&);
 
     static State stateFor(HTMLTreeBuilder*);
 
-    const State& state() const { return m_namespaceStack; }
-    void setState(const State& state) { m_namespaceStack = state; }
+    const State& state() const { return m_stack; }
+    void setState(const State& state) { m_stack = state; }
 
     SimulatedToken simulate(const CompactHTMLToken&, HTMLTokenizer*);
 
 private:
-    explicit HTMLTreeBuilderSimulator(HTMLTreeBuilder*);
-
-    bool inForeignContent() const { return m_namespaceStack.last() != HTML; }
+    bool inForeignContent() const { return currentNamespace() != HTML; }
+    Namespace currentNamespace() const { return static_cast<Namespace>(m_stack.last().ns); }
+    bool stackContainsNamespace(Namespace namespaceOfInterest) const
+    {
+        for (const auto& entry : m_stack) {
+            if (static_cast<Namespace>(entry.ns) == namespaceOfInterest)
+                return true;
+        }
+        return false;
+    }
 
     HTMLParserOptions m_options;
-    State m_namespaceStack;
+    State m_stack;
 };
 
 } // namespace blink