Revert of base: Fix DiscardableSharedMemory::mapped_size(). (patchset #2 id:20001 of https://codereview.chromium.org/842003002/)

Reason for revert:
Reverting this 2nd CL that touches discardable_shared_memory.

High levels of Windows crashes resulted from something in one of these two CLs (https://codereview.chromium.org/793443003 is the other).

Ref: https://crash.corp.google.com/browse?q=product.name%3D%27Chrome%27%20AND%20product.version%3D%2741.0.2271.0%27%20AND%20custom_data.ChromeCrashProto.ptype%3D%27renderer%27

Original issue's description:
> base: Fix DiscardableSharedMemory::mapped_size().
>
> Set |mapped_size_| to 0 after unmapping memory.
>
> BUG=429416
> TEST=base_unittests --gtest_filter=DiscardableSharedMemoryTest.MappedSize
>
> Committed: https://crrev.com/95bc5b1779dcf8e4a9e37ef600c0ea76293307e3
> Cr-Commit-Position: refs/heads/master@{#310625}

TBR=danakj@chromium.org,avi@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=429416

Review URL: https://codereview.chromium.org/810433003

Cr-Commit-Position: refs/heads/master@{#310916}

2 files changed, 0 insertions, 15 deletions

diff --git a/base/memory/discardable_shared_memory.cc b/base/memory/discardable_shared_memory.cc
index e04377e..2f80a16 100644
--- a/base/memory/discardable_shared_memory.cc
+++ b/base/memory/discardable_shared_memory.cc
@@ -353,7 +353,6 @@ bool DiscardableSharedMemory::IsMemoryResident() const {
 void DiscardableSharedMemory::Close() {
   shared_memory_.Unmap();
   shared_memory_.Close();
-  mapped_size_ = 0;
 }
 
 Time DiscardableSharedMemory::Now() const {
diff --git a/base/memory/discardable_shared_memory_unittest.cc b/base/memory/discardable_shared_memory_unittest.cc
index 896263d..90441e1 100644
--- a/base/memory/discardable_shared_memory_unittest.cc
+++ b/base/memory/discardable_shared_memory_unittest.cc
@@ -287,19 +287,5 @@ TEST(DiscardableSharedMemoryTest, LockAndUnlockRange) {
   EXPECT_TRUE(rv);
 }
 
-TEST(DiscardableSharedMemoryTest, MappedSize) {
-  const uint32 kDataSize = 1024;
-
-  TestDiscardableSharedMemory memory;
-  bool rv = memory.CreateAndMap(kDataSize);
-  ASSERT_TRUE(rv);
-
-  EXPECT_LE(kDataSize, memory.mapped_size());
-
-  // Mapped size should be 0 after memory segment has been closed.
-  memory.Close();
-  EXPECT_EQ(0u, memory.mapped_size());
-}
-
 }  // namespace
 }  // namespace base