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

runtime/vm/os_android.cc

 // Copyright (c) 2012, 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 "vm/globals.h"
 #if defined(TARGET_OS_ANDROID)
 
 #include "vm/os.h"
 
 #include <android/log.h>  // NOLINT
@@ skipping 161 matching lines @@
   // gettimeofday has microsecond resolution.
   struct timeval tv;
   if (gettimeofday(&tv, NULL) < 0) {
     UNREACHABLE();
     return 0;
   }
   return (static_cast<int64_t>(tv.tv_sec) * 1000000) + tv.tv_usec;
 }
 
 
+int64_t OS::GetCurrentTraceMicros() {
+  struct timespec ts;
+  if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
+    UNREACHABLE();
+    return 0;
+  }
+  // Convert to microseconds.
+  int64_t result = ts.tv_sec;
+  result *= kMicrosecondsPerSecond;
+  result += (ts.tv_nsec / kNanosecondsPerMicrosecond);
+  return result;
+}
+
+
 void* OS::AlignedAllocate(intptr_t size, intptr_t alignment) {
   const int kMinimumAlignment = 16;
   ASSERT(Utils::IsPowerOfTwo(alignment));
   ASSERT(alignment >= kMinimumAlignment);
   void* p = memalign(alignment, size);
   if (p == NULL) {
     UNREACHABLE();
   }
   return p;
 }
@@ skipping 250 matching lines @@
 }
 
 
 void OS::Exit(int code) {
   exit(code);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_ANDROID)