DevTools: Move usedHeapSize from TimelineEvent into counters.

LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt

Index: LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt
diff --git a/LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt b/LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt
index 03fe5fe98578145fb365d3a0419ac27120e6b5c0..0f219e368078ca11f8065f27c579daff0d24421a 100644
--- a/LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt
+++ b/LayoutTests/http/tests/inspector/timeline-xhr-event-expected.txt
@@ -12,7 +12,6 @@ XHRReadyStateChange Properties:
     frameId : <string>
     startTime : <number>
     type : "XHRReadyStateChange"
-    usedHeapSize : <number>
 }
 XHRReadyStateChange Properties:
 {
@@ -26,7 +25,6 @@ XHRReadyStateChange Properties:
     frameId : <string>
     startTime : <number>
     type : "XHRReadyStateChange"
-    usedHeapSize : <number>
 }
 XHRReadyStateChange Properties:
 {
@@ -40,7 +38,6 @@ XHRReadyStateChange Properties:
     frameId : <string>
     startTime : <number>
     type : "XHRReadyStateChange"
-    usedHeapSize : <number>
 }
 XHRLoad Properties:
 {
@@ -53,6 +50,5 @@ XHRLoad Properties:
     frameId : <string>
     startTime : <number>
     type : "XHRLoad"
-    usedHeapSize : <number>
 }