Make timeline use the same clock source as mojo's tracing infrastructure

runtime/vm/json_stream.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/json_stream.h"
 #include "vm/message.h"
@@ skipping 290 matching lines @@
   PrintCommaIfNeeded();
   buffer_.Printf("%" Pd64 "", i);
 }
 
 
 void JSONStream::PrintValueTimeMillis(int64_t millis) {
   PrintValue(static_cast<double>(millis));
 }
 
 
+void JSONStream::PrintValueTimeMicros(int64_t micros) {
+  PrintValue64(micros);
+}
+
+
 void JSONStream::PrintValue(double d) {
   PrintCommaIfNeeded();
   buffer_.Printf("%f", d);
 }
 
 
 static const char base64_digits[65] =
   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 static const char base64_pad = '=';
 
@@ skipping 137 matching lines @@
   PrintPropertyName(name);
   PrintValue64(i);
 }
 
 
 void JSONStream::PrintPropertyTimeMillis(const char* name, int64_t millis) {
   PrintProperty(name, static_cast<double>(millis));
 }
 
 
+void JSONStream::PrintPropertyTimeMicros(const char* name, int64_t micros) {
+  PrintProperty64(name, micros);
+}
+
+
 void JSONStream::PrintProperty(const char* name, double d) {
   PrintPropertyName(name);
   PrintValue(d);
 }
 
 
 void JSONStream::PrintProperty(const char* name, const char* s) {
   PrintPropertyName(name);
   PrintValue(s);
 }
@@ skipping 293 matching lines @@
   intptr_t len2 = OS::VSNPrint(p, len+1, format, args);
   va_end(args);
   ASSERT(len == len2);
   stream_->buffer_.AddChar('"');
   stream_->AddEscapedUTF8String(p);
   stream_->buffer_.AddChar('"');
   free(p);
 }
 
 }  // namespace dart