Revert of [XHR] Reduce 'readystatechange' event firing. (patchset #9 of

https://codereview.chromium.org/428473005/)

Reason for revert:
This change breaks legacy applications.

Original issue's description:
> [XHR] Reduce 'readystatechange' event firing.
> 
> Currently too many readystatechange events are fired and
> it hurts performance.
> 
> BUG=336066
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179381

Review URL: https://codereview.chromium.org/486133002

git-svn-id: svn://svn.chromium.org/blink/trunk@180554 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Source/core/xml/XMLHttpRequest.cpp

@@ -63,23 +63,12 @@
 #include "wtf/ArrayBuffer.h"
 #include "wtf/ArrayBufferView.h"
 #include "wtf/Assertions.h"
-#include "wtf/CurrentTime.h"
 #include "wtf/RefCountedLeakCounter.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/text/CString.h"
 
 namespace blink {
 
-// To throttle readystatechange event fired when readystatechange is not
-// changed, we don't dispatch the event within 50ms.
-// As dispatching readystatechange when readystatechange is NOT changed is not
-// specified, 50ms is not specified, too.
-// We choose this value because progress event is dispatched every 50ms, but
-// actually this value doesn't have to equal to the interval.
-// Note: When readystate is actually changed readystatechange event must be
-// dispatched no matter how recently dispatched the event was.
-const double readyStateChangeFireInterval = 0.05;
-
 DEFINE_DEBUG_ONLY_GLOBAL(WTF::RefCountedLeakCounter, xmlHttpRequestCounter, ("XMLHttpRequest"));
 
 static bool isSetCookieHeader(const AtomicString& name)
@@ -162,7 +151,6 @@ XMLHttpRequest::XMLHttpRequest(ExecutionContext* context, PassRefPtr<SecurityOri
     , m_progressEventThrottle(this)
     , m_responseTypeCode(ResponseTypeDefault)
     , m_securityOrigin(securityOrigin)
-    , m_previousReadyStateChangeFireTime(0)
     , m_async(true)
     , m_includeCredentials(false)
     , m_parsedResponse(false)
@@ -452,15 +440,12 @@ void XMLHttpRequest::trackProgress(int length)
     if (m_state != LOADING) {
         changeState(LOADING);
     } else {
-        // FIXME: Make our implementation and the spec consistent. This extra
-        // invocation of readystatechange event in LOADING state was needed
-        // when the progress event was not available.
-        double now = monotonicallyIncreasingTime();
-        bool shouldFire = now - m_previousReadyStateChangeFireTime >= readyStateChangeFireInterval;
-        if (shouldFire) {
-            m_previousReadyStateChangeFireTime = now;
-            dispatchReadyStateChangeEvent();
-        }
+        // Firefox calls readyStateChanged every time it receives data. Do
+        // the same to align with Firefox.
+        //
+        // FIXME: Make our implementation and the spec consistent. This
+        // behavior was needed when the progress event was not available.
+        dispatchReadyStateChangeEvent();
     }
 }
 

Source/core/xml/XMLHttpRequest.h

@@ -270,8 +270,6 @@ class XMLHttpRequest FINAL
     ResponseTypeCode m_responseTypeCode;
     RefPtr<SecurityOrigin> m_securityOrigin;
 
-    double m_previousReadyStateChangeFireTime;
-
     bool m_async;
     bool m_includeCredentials;
     // Used to skip m_responseDocument creation if it's done previously. We need