Add 'base::Time::Max()' to explicitly refer to the end of time.

BrowingDataRemover (and, I imagine, other systems) recognized ranges bounded by null Time objects ('base::Time()') as referring to "everything". That introduces easily-forgotten complexity, which leads to avoidable mistakes in logic. This CL provides a mechanism for avoiding this sort of confusion in the future by adding the ability to explicitly refer to the end of time via 'base::Time::Max()'.

It simply returns a Time object whose internal counter is set to the maximum int64, which means that simple comparisons like 'time <= end' will do The Right Thing™.

BUG=144972


Review URL: https://chromiumcodereview.appspot.com/10883061

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153514 0039d316-1c4b-4281-b951-d872f2087c98

base/time.cc

@@ -9,6 +9,8 @@
 #include <float.h>
 #endif
 
+#include <limits>
+
 #include "base/sys_string_conversions.h"
 #include "base/third_party/nspr/prtime.h"
 
@@ -63,6 +65,11 @@ int64 TimeDelta::InMicroseconds() const {
 
 // Time -----------------------------------------------------------------------
 
+// static
+Time Time::Max() {
+  return Time(std::numeric_limits<int64>::max());
+}
+
 // static
 Time Time::FromTimeT(time_t tt) {
   if (tt == 0)

base/time.h

@@ -254,6 +254,10 @@ class BASE_EXPORT Time {
   // times are increasing, or that two calls to Now() won't be the same.
   static Time Now();
 
+  // Returns the maximum time, which should be greater than any reasonable time
+  // with which we might compare it.
+  static Time Max();
+
   // Returns the current time. Same as Now() except that this function always
   // uses system time so that there are no discrepancies between the returned
   // time and system time even on virtual environments including our test bot.

base/time_unittest.cc

@@ -479,6 +479,12 @@ TEST_F(TimeTest, ExplodeBeforeUnixEpoch) {
   EXPECT_EQ(1, exploded.millisecond);
 }
 
+TEST_F(TimeTest, Max) {
+  EXPECT_EQ(base::Time::Max(), base::Time::Max());
+  EXPECT_GT(base::Time::Max(), base::Time::Now());
+  EXPECT_GT(base::Time::Max(), base::Time());
+}
+
 TEST(TimeTicks, Deltas) {
   for (int index = 0; index < 50; index++) {
     TimeTicks ticks_start = TimeTicks::Now();