Revert of DevTools: respond with error when Debugger command is sent to disabled debugger agent

Source/core/inspector/InspectorDOMDebuggerAgent.cpp

Index: Source/core/inspector/InspectorDOMDebuggerAgent.cpp
diff --git a/Source/core/inspector/InspectorDOMDebuggerAgent.cpp b/Source/core/inspector/InspectorDOMDebuggerAgent.cpp
index 03df74b79870e84e38ef0b122a29fd492e8b1c02..0300bf496bbc7a64f55ccd007f70d7fde383c7cc 100644
--- a/Source/core/inspector/InspectorDOMDebuggerAgent.cpp
+++ b/Source/core/inspector/InspectorDOMDebuggerAgent.cpp
@@ -146,19 +146,6 @@
     disable(nullptr);
 }
 
-bool InspectorDOMDebuggerAgent::checkEnabled(ErrorString* errorString)
-{
-    if (!m_domAgent->enabled()) {
-        *errorString = "DOM domain required by DOMDebugger is not enabled";
-        return false;
-    }
-    if (!m_debuggerAgent->enabled()) {
-        *errorString = "Debugger domain required by DOMDebugger is not enabled";
-        return false;
-    }
-    return true;
-}
-
 void InspectorDOMDebuggerAgent::disable(ErrorString*)
 {
     m_instrumentingAgents->setInspectorDOMDebuggerAgent(nullptr);
@@ -196,12 +183,18 @@
 
 void InspectorDOMDebuggerAgent::setBreakpoint(ErrorString* error, const String& eventName, const String* targetName)
 {
-    if (!checkEnabled(error))
-        return;
     if (eventName.isEmpty()) {
         *error = "Event name is empty";
         return;
     }
+
+    // Backward compatibility. Some extensions expect that DOMDebuggerAgent is always enabled.
+    // See https://stackoverflow.com/questions/25764336/chrome-extension-domdebugger-api-does-not-work-anymore
+    if (!m_domAgent->enabled())
+        m_domAgent->enable(error);
+
+    if (error->length())
+        return;
 
     RefPtr<JSONObject> eventListenerBreakpoints = m_state->getObject(DOMDebuggerAgentState::eventListenerBreakpoints);
     RefPtr<JSONObject> breakpointsByTarget = ensurePropertyObject(eventListenerBreakpoints.get(), eventName);
@@ -300,8 +293,6 @@
 
 void InspectorDOMDebuggerAgent::setDOMBreakpoint(ErrorString* errorString, int nodeId, const String& typeString)
 {
-    if (!checkEnabled(errorString))
-        return;
     Node* node = m_domAgent->assertNode(errorString, nodeId);
     if (!node)
         return;
@@ -320,8 +311,6 @@
 
 void InspectorDOMDebuggerAgent::removeDOMBreakpoint(ErrorString* errorString, int nodeId, const String& typeString)
 {
-    if (!checkEnabled(errorString))
-        return;
     Node* node = m_domAgent->assertNode(errorString, nodeId);
     if (!node)
         return;
@@ -617,10 +606,8 @@
         didFireWebGLWarning();
 }
 
-void InspectorDOMDebuggerAgent::setXHRBreakpoint(ErrorString* errorString, const String& url)
-{
-    if (!checkEnabled(errorString))
-        return;
+void InspectorDOMDebuggerAgent::setXHRBreakpoint(ErrorString*, const String& url)
+{
     if (url.isEmpty()) {
         m_state->setBoolean(DOMDebuggerAgentState::pauseOnAllXHRs, true);
         return;
@@ -631,7 +618,7 @@
     m_state->setObject(DOMDebuggerAgentState::xhrBreakpoints, xhrBreakpoints.release());
 }
 
-void InspectorDOMDebuggerAgent::removeXHRBreakpoint(ErrorString* errorString, const String& url)
+void InspectorDOMDebuggerAgent::removeXHRBreakpoint(ErrorString*, const String& url)
 {
     if (url.isEmpty()) {
         m_state->setBoolean(DOMDebuggerAgentState::pauseOnAllXHRs, false);