Implement device-ram client hints header

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

Index: third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
diff --git a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
index c71f73dd74430bd4a9f6b700dadfd961078d83fb..4e2b8f2599d54d0235d3df2e5218cef785ed6f4a 100644
--- a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
@@ -606,6 +606,22 @@ void FrameFetchContext::ModifyRequestForCSP(ResourceRequest& resource_request) {
   GetFrame()->Loader().ModifyRequestForCSP(resource_request, GetDocument());
 }
 
+float FrameFetchContext::ClientHintsDeviceRAM(int physical_memory_mb) {
+  // TODO(fmeawad): The calculations in this method are still evolving as the
+  // spec gets updated: https://github.com/WICG/device-ram The reported
+  // device-ram is rounded down to next power of 2 in GB. Ex. 3072MB will return
+  // 2, and 768MB will return 0.5.
+  DCHECK_GT(physical_memory_mb, 0);
+  int power = -1;  // To compensate of the extra loop iteration.
+  // Extract the MSB location.
+  while (physical_memory_mb != 0) {
+    physical_memory_mb >>= 1;
+    power++;
+  }

[Yoav Weiss, 2017/05/26 05:44:22]

```
int power = 0;
// Extract the MSB location.
while (physical_memory_mb > 1) {
  physical_memory_mb >>= 1;
  power++;
}
```

gives you the same end result, is less confusing and performs one less
iteration.

[fmeawad, 2017/05/26 20:13:16]

Done. and thank you for your patience.

+  // Restore to the power of 2, and convert to GB.
+  return (float)(1 << power) / (float)1024.0;

[Yoav Weiss, 2017/05/26 05:44:22]

static_cast<float>() would be better for the first. No need to cast the second,
as 1024.0 is already a float.

[fmeawad, 2017/05/26 20:13:16]

Done.

+}
+
 void FrameFetchContext::AddClientHintsIfNecessary(
     const ClientHintsPreferences& hints_preferences,
     const FetchParameters::ResourceWidth& resource_width,
@@ -613,6 +629,9 @@ void FrameFetchContext::AddClientHintsIfNecessary(
   if (!RuntimeEnabledFeatures::clientHintsEnabled() || !GetDocument())
     return;
 
+  bool should_send_device_ram =
+      GetDocument()->GetClientHintsPreferences().ShouldSendDeviceRAM() ||
+      hints_preferences.ShouldSendDeviceRAM();
   bool should_send_dpr =
       GetDocument()->GetClientHintsPreferences().ShouldSendDPR() ||
       hints_preferences.ShouldSendDPR();
@@ -623,6 +642,13 @@ void FrameFetchContext::AddClientHintsIfNecessary(
       GetDocument()->GetClientHintsPreferences().ShouldSendViewportWidth() ||
       hints_preferences.ShouldSendViewportWidth();
 
+  if (should_send_device_ram) {
+    int physical_memory = Platform::Current()->AmountOfPhysicalMemoryMB();
+    request.AddHTTPHeaderField(
+        "device-ram",
+        AtomicString(String::Number(ClientHintsDeviceRAM(physical_memory))));
+  }
+
   if (should_send_dpr) {
     request.AddHTTPHeaderField(
         "DPR", AtomicString(String::Number(GetDocument()->DevicePixelRatio())));