[DeviceMemory] Limit the possibile reported value by the DeviceMemory…

… APIs

In this CL, we revert back to using a single most significant bit
instead of 2 bits (i.e. resulting values should only be powers of 2).

We also limit the max reported value to 8GB, beyond that the value is
not relevant.

Bug: 718622
Change-Id: Id83482a4b77dd3f6b8c49af34029564ab20dd8fe
Reviewed-on: https://chromium-review.googlesource.com/717020
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Shubhie Panicker <panicker@chromium.org>
Commit-Queue: Fadi Meawad <fmeawad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508561}

third_party/WebKit/Source/core/loader/FrameFetchContextTest.cpp

@@ -527,9 +527,9 @@ TEST_F(FrameFetchContextHintsTest, MonitorDeviceMemoryHints) {
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(2048);
   ExpectHeader("http://www.example.com/1.gif", "Device-Memory", true, "2");
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(64385);
-  ExpectHeader("http://www.example.com/1.gif", "Device-Memory", true, "64");
+  ExpectHeader("http://www.example.com/1.gif", "Device-Memory", true, "8");
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(768);
-  ExpectHeader("http://www.example.com/1.gif", "Device-Memory", true, "0.75");
+  ExpectHeader("http://www.example.com/1.gif", "Device-Memory", true, "0.5");
   ExpectHeader("http://www.example.com/1.gif", "DPR", false, "");
   ExpectHeader("http://www.example.com/1.gif", "Width", false, "");
   ExpectHeader("http://www.example.com/1.gif", "Viewport-Width", false, "");

third_party/WebKit/common/device_memory/approximated_device_memory.cc

@@ -34,13 +34,13 @@ void ApproximatedDeviceMemory::CalculateAndSetApproximatedDeviceMemory() {
   int lower_bound = physical_memory_mb_;
   int power = 0;
 
-  // Extract the most significant 2-bits and their location.
-  while (lower_bound >= 4) {
+  // Extract the most-significant-bit and its location.
+  while (lower_bound > 1) {
     lower_bound >>= 1;
     power++;
   }
-  // The lower_bound value is either 0b10 or 0b11.
-  DCHECK(lower_bound & 2);
+  // The remaining should always be equal to exactly 1.
+  DCHECK_EQ(lower_bound, 1);
 
   int64_t upper_bound = lower_bound + 1;
   lower_bound = lower_bound << power;
@@ -51,6 +51,11 @@ void ApproximatedDeviceMemory::CalculateAndSetApproximatedDeviceMemory() {
     approximated_device_memory_gb_ = static_cast<float>(lower_bound) / 1024.0;
   else
     approximated_device_memory_gb_ = static_cast<float>(upper_bound) / 1024.0;
+
+  // The exact value beyond 8GB is irrelvant, hence we max-limit the reported
+  // value to 8GB.
+  if (approximated_device_memory_gb_ > 8)
+    approximated_device_memory_gb_ = 8.0;
 }
 
 // static

third_party/WebKit/common/device_memory/approximated_device_memory_unittest.cc

@@ -24,29 +24,29 @@ TEST_F(ApproximatedDeviceMemoryTest, GetApproximatedDeviceMemory) {
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(640);  // 512+128MB
   EXPECT_EQ(0.5, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(768);  // 512+256MB
-  EXPECT_EQ(0.75, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(0.5, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(1000);  // <1GB
   EXPECT_EQ(1, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(1024);  // 1GB
   EXPECT_EQ(1, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(1536);  // 1.5GB
-  EXPECT_EQ(1.5, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(1, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(2000);  // <2GB
   EXPECT_EQ(2, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(2048);  // 2GB
   EXPECT_EQ(2, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(3000);  // <3GB
-  EXPECT_EQ(3, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(2, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(5120);  // 5GB
   EXPECT_EQ(4, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(8192);  // 8GB
   EXPECT_EQ(8, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(16384);  // 16GB
-  EXPECT_EQ(16, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(8, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(32768);  // 32GB
-  EXPECT_EQ(32, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(8, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
   ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(64385);  // <64GB
-  EXPECT_EQ(64, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
+  EXPECT_EQ(8, ApproximatedDeviceMemory::GetApproximatedDeviceMemory());
 }
 
 }  // namespace