Fixes pinch-to-zoom when linking against the 10.11 SDK or newer.

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index 98d344535040c84c37473567d953ab94dec8a512..3b0efc11303a4859cf6cd371d2d7b6933c685dff 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -150,7 +150,8 @@ RenderWidgetHostView* GetRenderWidgetHostViewToUse(
                    consumed:(BOOL)consumed;
 - (void)processedGestureScrollEvent:(const blink::WebGestureEvent&)event
                            consumed:(BOOL)consumed;
-
+- (void)handleBeginGestureWithEvent:(NSEvent*)event;
+- (void)handleEndGestureWithEvent:(NSEvent*)event;
 - (void)keyEvent:(NSEvent*)theEvent wasKeyEquivalent:(BOOL)equiv;
 - (void)windowDidChangeBackingProperties:(NSNotification*)notification;
 - (void)windowChangedGlobalFrame:(NSNotification*)notification;
@@ -2278,7 +2279,13 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   }
 }
 
-- (void)beginGestureWithEvent:(NSEvent*)event {
+// Internal implementation for handling begin gesture events.  This helper
+// method is called via different codepaths based on OS version and SDK:
+// - On 10.11 and later, when linking with the 10.11 SDK, it is called from
+//   |magnifyWithEvent:| when the given event's phase is NSEventPhaseBegin.
+// - On 10.10 and earlier, or when linking with an earlier SDK, it is called
+//   by |beginGestureWithEvent:| when a gesture begins.
+- (void)handleBeginGestureWithEvent:(NSEvent*)event {
   [responderDelegate_ beginGestureWithEvent:event];
   gestureBeginEvent_.reset(
       new WebGestureEvent(WebGestureEventBuilder::Build(event, self)));
@@ -2291,7 +2298,13 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   }
 }
 
-- (void)endGestureWithEvent:(NSEvent*)event {
+// Internal implementation for handling end gesture events.  This helper
+// method is called via different codepaths based on OS version and SDK:
+// - On 10.11 and later, when linking with the 10.11 SDK, it is called from
+//   |magnifyWithEvent:| when the given event's phase is NSEventPhaseEnded.
+// - On 10.10 and earlier, or when linking with an earlier SDK, it is called
+//   by |endGestureWithEvent:| when a gesture ends.
+- (void)handleEndGestureWithEvent:(NSEvent*)event {
   [responderDelegate_ endGestureWithEvent:event];
   gestureBeginEvent_.reset();
 
@@ -2306,6 +2319,38 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   }
 }
 
+- (void)beginGestureWithEvent:(NSEvent*)event {
+  // This method must be handled when linking with the 10.10 SDK or earlier, or
+  // when the app is running on 10.10 or earlier.  In other circumstances, the
+  // event will be handled by |magnifyWithEvent:|, so this method should do
+  // nothing.
+  bool shouldHandle = true;
+#if defined(MAC_OS_X_VERSION_10_11) && \
+    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_11
+  shouldHandle = base::mac::IsAtMostOS10_10();
+#endif
+
+  if (shouldHandle) {
+    [self handleBeginGestureWithEvent:event];
+  }
+}
+
+- (void)endGestureWithEvent:(NSEvent*)event {
+  // This method must be handled when linking with the 10.10 SDK or earlier, or
+  // when the app is running on 10.10 or earlier.  In other circumstances, the
+  // event will be handled by |magnifyWithEvent:|, so this method should do
+  // nothing.
+  bool shouldHandle = true;
+#if defined(MAC_OS_X_VERSION_10_11) && \
+    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_11
+  shouldHandle = base::mac::IsAtMostOS10_10();
+#endif
+
+  if (shouldHandle) {
+    [self handleEndGestureWithEvent:event];
+  }
+}
+
 - (void)touchesMovedWithEvent:(NSEvent*)event {
   [responderDelegate_ touchesMovedWithEvent:event];
 }
@@ -2503,6 +2548,23 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   if (!renderWidgetHostView_->render_widget_host_)
     return;
 
+// When linking against the 10.11 (or later) SDK and running on 10.11 or later,
+// check the phase of the event and specially handle the "begin" and "end"
+// phases.
+#if defined(MAC_OS_X_VERSION_10_11) && \
+    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_11
+  if (event.phase == NSEventPhaseBegan) {
+    [self handleBeginGestureWithEvent:event];
+    return;
+  }
+
+  if (event.phase == NSEventPhaseEnded ||
+             event.phase == NSEventPhaseCancelled) {
+    [self handleEndGestureWithEvent:event];
+    return;
+  }
+#endif
+
   // If, due to nesting of multiple gestures (e.g, from multiple touch
   // devices), the beginning of the gesture has been lost, skip the remainder
   // of the gesture.