Canvas2d: Make the intersection computation O(1) instead of O(n) in ClipList.

third_party/WebKit/Source/modules/canvas2d/ClipList.cpp

Index: third_party/WebKit/Source/modules/canvas2d/ClipList.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/ClipList.cpp b/third_party/WebKit/Source/modules/canvas2d/ClipList.cpp
index 7443df76139ab1d397f736ea4ea94cd9e9e761b8..37b07a42067387a5c3878e2caf1081c579d0626c 100644
--- a/third_party/WebKit/Source/modules/canvas2d/ClipList.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/ClipList.cpp
@@ -18,6 +18,10 @@ void ClipList::clipPath(const SkPath& path, AntiAliasingMode antiAliasingMode, c
     newClip.m_antiAliasingMode = antiAliasingMode;
     newClip.m_path = path;
     newClip.m_path.transform(ctm);
+    if (m_clipList.isEmpty())
+        m_currentClipPath = path;
+    else
+        Op(m_currentClipPath, path, SkPathOp::kIntersect_SkPathOp, &m_currentClipPath);
     m_clipList.append(newClip);
 }
 
@@ -28,13 +32,9 @@ void ClipList::playback(SkCanvas* canvas) const
     }
 }
 
-SkPath ClipList::intersectPathWithClip(const SkPath& path) const
+const SkPath& ClipList::getCurrentClipPath() const
 {
-    SkPath total = path;
-    for (const ClipOp* it = m_clipList.begin(); it < m_clipList.end(); it++) {
-        Op(total, it->m_path, SkPathOp::kIntersect_SkPathOp, &total);
-    }
-    return total;
+    return m_currentClipPath;
 }
 
 ClipList::ClipOp::ClipOp()