[DevTools] Explicitly enable/disable Page.viewportChanged protocol event.

Source/core/inspector/InspectorPageAgent.cpp

Index: Source/core/inspector/InspectorPageAgent.cpp
diff --git a/Source/core/inspector/InspectorPageAgent.cpp b/Source/core/inspector/InspectorPageAgent.cpp
index 57483985c9b9a8f6112b28889f8934e7d6bfb976..77cc78f41a9898632c3cae10ce046b2fcc121c5b 100644
--- a/Source/core/inspector/InspectorPageAgent.cpp
+++ b/Source/core/inspector/InspectorPageAgent.cpp
@@ -105,6 +105,7 @@ static const char touchEventEmulationEnabled[] = "touchEventEmulationEnabled";
 static const char pageAgentEmulatedMedia[] = "pageAgentEmulatedMedia";
 static const char showSizeOnResize[] = "showSizeOnResize";
 static const char showGridOnResize[] = "showGridOnResize";
+static const char viewportChangedEventEnabled[] = "viewportChangedEventEnabled";
 }
 
 namespace {
@@ -817,6 +818,15 @@ void InspectorPageAgent::setDeviceMetricsOverride(ErrorString* errorString, int
     updateViewMetricsFromState();
 }
 
+void InspectorPageAgent::setViewportChangedEventEnabled(ErrorString*, bool enabled)
+{
+    if (m_state->getBoolean(PageAgentState::viewportChangedEventEnabled) != enabled) {
+        m_state->setBoolean(PageAgentState::viewportChangedEventEnabled, enabled);
+        if (enabled)
+            viewportChanged();
+    }
+}
+
 void InspectorPageAgent::clearDeviceMetricsOverride(ErrorString*)
 {
     if (m_state->getBoolean(PageAgentState::deviceMetricsOverrideEnabled)) {
@@ -1166,7 +1176,7 @@ void InspectorPageAgent::didScroll()
 
 void InspectorPageAgent::viewportChanged()
 {
-    if (!m_enabled)
+    if (!m_enabled || !m_state->getBoolean(PageAgentState::viewportChangedEventEnabled))
         return;
     IntSize contentsSize = m_page->deprecatedLocalMainFrame()->view()->contentsSize();
     IntRect viewRect = m_page->deprecatedLocalMainFrame()->view()->visibleContentRect();