Increase timer resolution

Now that site isolation is enabled on desktop platforms, we can safely
increase timer resolution back to the previous 5µs value. Clock edge
jittering is still enabled however.

Bug: 798795, 422000
Change-Id: I23f29a40a8615354674f33bae7339d348773dd00
Reviewed-on: https://chromium-review.googlesource.com/c/1290916Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601536}

gin/v8_platform.cc

@@ -114,7 +114,13 @@ base::LazyInstance<EnabledStateObserverImpl>::Leaky g_trace_state_dispatcher =
 // TODO(skyostil): Deduplicate this with the clamper in Blink.
 class TimeClamper {
  public:
-  static constexpr double kResolutionSeconds = 0.001;
+// As site isolation is enabled on desktop platforms, we can safely provide
+// more timing resolution. Jittering is still enabled everywhere.
+#if defined(OS_ANDROID)
+  static constexpr double kResolutionSeconds = 100e-6;
+#else
+  static constexpr double kResolutionSeconds = 5e-6;
+#endif
 
   TimeClamper() : secret_(base::RandUint64()) {}
 

third_party/blink/renderer/core/timing/time_clamper.h

@@ -6,6 +6,7 @@
 #define THIRD_PARTY_BLINK_RENDERER_CORE_TIMING_TIME_CLAMPER_H_
 
 #include "base/macros.h"
+#include "build/build_config.h"
 #include "third_party/blink/renderer/core/core_export.h"
 
 #include <stdint.h>
@@ -14,11 +15,17 @@ namespace blink {
 
 class CORE_EXPORT TimeClamper {
  public:
-  static constexpr double kResolutionSeconds = 0.0001;
+// As site isolation is enabled on desktop platforms, we can safely provide
+// more timing resolution. Jittering is still enabled everywhere.
+#if defined(OS_ANDROID)
+  static constexpr double kResolutionSeconds = 100e-6;
+#else
+  static constexpr double kResolutionSeconds = 5e-6;
+#endif
 
   TimeClamper();
 
-  // Deterministically clamp the time value |time_seconds| to a 100us interval
+  // Deterministically clamp the time value |time_seconds| to a fixed interval
   // to prevent timing attacks. See
   // http://www.w3.org/TR/hr-time-2/#privacy-security.
   //