cc: Turn overdraw metrics on only when about:tracing is recording.

cc/overdraw_metrics.cc

Index: cc/overdraw_metrics.cc
diff --git a/cc/overdraw_metrics.cc b/cc/overdraw_metrics.cc
index be8e7f83cbbbd5fe747c8d76f327bab2b94d7062..1f8aed8dc8adf8f5141cd4f32a78faf404850755 100644
--- a/cc/overdraw_metrics.cc
+++ b/cc/overdraw_metrics.cc
@@ -33,32 +33,6 @@ OverdrawMetrics::OverdrawMetrics(bool recordMetricsForFrame)
 {
 }
 
-static inline float wedgeProduct(const gfx::PointF& p1, const gfx::PointF& p2)
-{
-    return p1.x() * p2.y() - p1.y() * p2.x();
-}
-
-// Calculates area of an arbitrary convex polygon with up to 8 points.
-static inline float polygonArea(const gfx::PointF points[8], int numPoints)
-{
-    if (numPoints < 3)
-        return 0;
-
-    float area = 0;
-    for (int i = 0; i < numPoints; ++i)
-        area += wedgeProduct(points[i], points[(i+1)%numPoints]);
-    return fabs(0.5f * area);
-}
-
-// Takes a given quad, maps it by the given transformation, and gives the area of the resulting polygon.
-static inline float areaOfMappedQuad(const WebTransformationMatrix& transform, const gfx::QuadF& quad)
-{
-    gfx::PointF clippedQuad[8];
-    int numVerticesInClippedQuad = 0;
-    MathUtil::mapClippedQuad(transform, quad, clippedQuad, numVerticesInClippedQuad);
-    return polygonArea(clippedQuad, numVerticesInClippedQuad);
-}
-
 void OverdrawMetrics::didPaint(const gfx::Rect& paintedRect)
 {
     if (!m_recordMetricsForFrame)
@@ -78,8 +52,10 @@ void OverdrawMetrics::didUpload(const WebTransformationMatrix& transformToTarget
     if (!m_recordMetricsForFrame)
         return;
 
-    float uploadArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(uploadRect));
-    float uploadOpaqueArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(gfx::IntersectRects(opaqueRect, uploadRect)));
+    gfx::Rect uploadOpaqueRect = gfx::IntersectRects(opaqueRect, uploadRect);
+
+    float uploadArea = static_cast<float>(uploadRect.width()) * uploadRect.height();
+    float uploadOpaqueArea = static_cast<float>(uploadOpaqueRect.width()) * uploadOpaqueRect.height();
 
     m_pixelsUploadedOpaque += uploadOpaqueArea;
     m_pixelsUploadedTranslucent += uploadArea - uploadOpaqueArea;
@@ -106,8 +82,8 @@ void OverdrawMetrics::didCullForDrawing(const WebTransformationMatrix& transform
     if (!m_recordMetricsForFrame)
         return;
 
-    float beforeCullArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(beforeCullRect));
-    float afterCullArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(afterCullRect));
+    float beforeCullArea = static_cast<float>(beforeCullRect.width()) * beforeCullRect.height();
+    float afterCullArea = static_cast<float>(afterCullRect.width()) * afterCullRect.height();
 
     m_pixelsCulledForDrawing += beforeCullArea - afterCullArea;
 }
@@ -117,8 +93,10 @@ void OverdrawMetrics::didDraw(const WebTransformationMatrix& transformToTarget,
     if (!m_recordMetricsForFrame)
         return;
 
-    float afterCullArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(afterCullRect));
-    float afterCullOpaqueArea = areaOfMappedQuad(transformToTarget, gfx::QuadF(gfx::IntersectRects(opaqueRect, afterCullRect)));
+    gfx::Rect afterCullOpaqueRect = gfx::IntersectRects(opaqueRect, afterCullRect);
+
+    float afterCullArea = static_cast<float>(afterCullRect.width()) * afterCullRect.height();
+    float afterCullOpaqueArea = static_cast<float>(afterCullOpaqueRect.width()) * afterCullOpaqueRect.height();
 
     m_pixelsDrawnOpaque += afterCullOpaqueArea;
     m_pixelsDrawnTranslucent += afterCullArea - afterCullOpaqueArea;