[DOMStorage] Rate limiting writes to disk.

Given access patterns that are just wrong, local & session storage can write many gigabytes per day or keep the disk perpetually spun up. To avoid excessive IO, we apply limits to the amount of data being written and the frequency of writes to address both kinds of 'bad' behaviors.

TBR=rvargas
BUG=176727

Review URL: https://codereview.chromium.org/896643002

Cr-Commit-Position: refs/heads/master@{#317424}

2 files changed, 17 insertions, 0 deletions

diff --git a/base/time/time.h b/base/time/time.h
index 18de085..6d61861 100644
--- a/base/time/time.h
+++ b/base/time/time.h
@@ -178,6 +178,14 @@ class BASE_EXPORT TimeDelta {
     return delta_ / a.delta_;
   }
 
+  // Multiplicative computations with floats.
+  TimeDelta multiply_by(double a) const {
+    return TimeDelta(delta_ * a);
+  }
+  TimeDelta divide_by(double a) const {
+    return TimeDelta(delta_ / a);
+  }
+
   // Defined below because it depends on the definition of the other classes.
   Time operator+(Time t) const;
   TimeTicks operator+(TimeTicks t) const;
diff --git a/base/time/time_unittest.cc b/base/time/time_unittest.cc
index fdac59d..6387ec7 100644
--- a/base/time/time_unittest.cc
+++ b/base/time/time_unittest.cc
@@ -867,6 +867,15 @@ TEST(TimeDelta, Magnitude) {
             TimeDelta::FromMicroseconds(min_int64_plus_two).magnitude());
 }
 
+
+TEST(TimeDelta, multiply_by) {
+  double d = 0.5;
+  EXPECT_EQ(TimeDelta::FromMilliseconds(500),
+            TimeDelta::FromMilliseconds(1000).multiply_by(d));
+  EXPECT_EQ(TimeDelta::FromMilliseconds(2000),
+            TimeDelta::FromMilliseconds(1000).divide_by(d));
+}
+
 TEST(TimeDeltaLogging, DCheckEqCompiles) {
   DCHECK_EQ(TimeDelta(), TimeDelta());
 }