[Mac] Respect natural/inverted scroll direction on Lion when gesturing.

chrome/browser/ui/cocoa/browser_window_controller.mm

Index: chrome/browser/ui/cocoa/browser_window_controller.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_controller.mm b/chrome/browser/ui/cocoa/browser_window_controller.mm
index 6e4a26ae3e6c2017a59688886d76f1bc2f4fb8eb..e8aaf325ec0d5b576754f54f06eceedbecaa657c 100644
--- a/chrome/browser/ui/cocoa/browser_window_controller.mm
+++ b/chrome/browser/ui/cocoa/browser_window_controller.mm
@@ -1673,13 +1673,23 @@ typedef NSInteger NSWindowAnimationBehavior;
 // Documented in 10.6+, but present starting in 10.5. Called when we get a
 // three-finger swipe.
 - (void)swipeWithEvent:(NSEvent*)event {
+  CGFloat deltaX = [event deltaX];
+  CGFloat deltaY = [event deltaY];
+
+  // On Lion, the user can choose to use a "natural" scroll direction with
+  // inverted axes.
+  if ([self isScrollDirectionInverted]) {
+    deltaX *= -1;
+    deltaY *= -1;
+  }
+
   // Map forwards and backwards to history; left is positive, right is negative.
   unsigned int command = 0;
-  if ([event deltaX] > 0.5) {
+  if (deltaX > 0.5) {
     command = IDC_BACK;
-  } else if ([event deltaX] < -0.5) {
+  } else if (deltaX < -0.5) {
     command = IDC_FORWARD;
-  } else if ([event deltaY] > 0.5) {
+  } else if (deltaY > 0.5) {
     // TODO(pinkerton): figure out page-up, http://crbug.com/16305
   } else if ([event deltaY] < -0.5) {
     // TODO(pinkerton): figure out page-down, http://crbug.com/16305
@@ -1787,6 +1797,11 @@ typedef NSInteger NSWindowAnimationBehavior;
     return;
 
   CGFloat sum = std::accumulate(magnitudes.begin(), magnitudes.end(), 0.0f);
+  // On Lion, the user can choose to use a "natural" scroll direction with
+  // inverted axes.
+  if ([self isScrollDirectionInverted])
+    sum *= -1;
+
   int command_id = 0;
   if (sum > 0.3)
     command_id = IDC_FORWARD;