Add Blink support for showing image placeholders using range requests.

third_party/WebKit/Source/core/fetch/Resource.cpp

Index: third_party/WebKit/Source/core/fetch/Resource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/Resource.cpp b/third_party/WebKit/Source/core/fetch/Resource.cpp
index 6339c15de125e22e0b0539b8f6b894db9052f657..99b3a6c1ae4ee926278f0dff83d3cfa5c23981e2 100644
--- a/third_party/WebKit/Source/core/fetch/Resource.cpp
+++ b/third_party/WebKit/Source/core/fetch/Resource.cpp
@@ -932,6 +932,10 @@ void Resource::setLoFiStateOff() {
   m_resourceRequest.setLoFiState(WebURLRequest::LoFiOff);
 }
 
+void Resource::clearRangeRequestHeader() {

[Nate Chapin, 2016/10/18 18:23:17]

Potentially out of scope nit: I don't like that we need to add a new method on
Resource every time we want to modify a header. We should consider adding a
protected Resource::mutableResourceRequest() for the Resource subclasses that
need to modify m_resourceRequest.

[sclittle, 2016/10/18 23:53:03]

I agree completely, plus I'll be modifying it even more in a later CL I add the
request bit to make the embedder return the full cached resource if it's all
there and fresh. Do you mind if I make that Resource::mutableResourceRequest()
change in a follow up CL?

+  m_resourceRequest.clearHTTPHeaderField("range");
+}
+
 void Resource::revalidationSucceeded(
     const ResourceResponse& validatingResponse) {
   SECURITY_CHECK(m_redirectChain.isEmpty());