Use the constants defined in HTTPNames where possible

Bug: 
Change-Id: Ia32d500ba42bdd485f0c35e1a34659332002a162
Reviewed-on: https://chromium-review.googlesource.com/648909
Commit-Queue: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517760}

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

@@ -45,6 +45,7 @@
 #include "platform/heap/Handle.h"
 #include "platform/network/EncodedFormData.h"
 #include "platform/network/FormDataEncoder.h"
+#include "platform/network/http_names.h"
 #include "platform/wtf/CurrentTime.h"
 #include "platform/wtf/text/StringBuilder.h"
 #include "platform/wtf/text/TextEncoding.h"
@@ -293,7 +294,7 @@ FrameLoadRequest FormSubmission::CreateFrameLoadRequest(
     frame_request.SetFrameName(target_);
 
   if (method_ == FormSubmission::kPostMethod) {
-    frame_request.GetResourceRequest().SetHTTPMethod("POST");
+    frame_request.GetResourceRequest().SetHTTPMethod(HTTPNames::POST);
     frame_request.GetResourceRequest().SetHTTPBody(form_data_);
 
     // construct some user headers if necessary

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

@@ -79,6 +79,7 @@
 #include "platform/loader/fetch/fetch_initiator_type_names.h"
 #include "platform/mhtml/MHTMLArchive.h"
 #include "platform/network/NetworkStateNotifier.h"
+#include "platform/network/http_names.h"
 #include "platform/scheduler/child/web_scheduler.h"
 #include "platform/scheduler/renderer/web_view_scheduler.h"
 #include "platform/weborigin/SchemeRegistry.h"
@@ -374,8 +375,8 @@ mojom::FetchCacheMode FrameFetchContext::ResourceRequestCachePolicy(
   DCHECK(GetFrame());
   if (type == Resource::kMainResource) {
     const auto cache_mode = DetermineCacheMode(
-        request.HttpMethod() == "POST" ? RequestMethod::kIsPost
-                                       : RequestMethod::kIsNotPost,
+        request.HttpMethod() == HTTPNames::POST ? RequestMethod::kIsPost
+                                                : RequestMethod::kIsNotPost,
         request.IsConditional() ? RequestType::kIsConditional
                                 : RequestType::kIsNotConditional,
         ResourceType::kIsMainResource, MasterDocumentLoader()->LoadType());

third_party/WebKit/Source/core/loader/resource/ImageResourceTest.cpp

@@ -45,6 +45,7 @@
 #include "platform/loader/fetch/UniqueIdentifier.h"
 #include "platform/loader/testing/MockFetchContext.h"
 #include "platform/loader/testing/MockResourceClient.h"
+#include "platform/network/http_names.h"
 #include "platform/scheduler/test/fake_web_task_runner.h"
 #include "platform/testing/RuntimeEnabledFeaturesTestHelpers.h"
 #include "platform/testing/ScopedMockedURL.h"
@@ -1410,7 +1411,7 @@ TEST(ImageResourceTest, FetchAllowPlaceholderPostRequest) {
   KURL test_url(kTestURL);
   ScopedMockedURLLoad scoped_mocked_url_load(test_url, GetTestFilePath());
   ResourceRequest resource_request(test_url);
-  resource_request.SetHTTPMethod("POST");
+  resource_request.SetHTTPMethod(HTTPNames::POST);
   FetchParameters params(resource_request);
   params.SetAllowImagePlaceholder();
   ImageResource* image_resource = ImageResource::Fetch(params, CreateFetcher());

third_party/WebKit/Source/platform/loader/fetch/FetchUtils.cpp

@@ -78,7 +78,8 @@ const ForbiddenHeaderNames& ForbiddenHeaderNames::Get() {
 bool FetchUtils::IsCORSSafelistedMethod(const String& method) {
   // https://fetch.spec.whatwg.org/#cors-safelisted-method
   // "A CORS-safelisted method is a method that is `GET`, `HEAD`, or `POST`."
-  return method == "GET" || method == "HEAD" || method == "POST";
+  return method == HTTPNames::GET || method == HTTPNames::HEAD ||
+         method == HTTPNames::POST;
 }
 
 bool FetchUtils::IsCORSSafelistedHeader(const AtomicString& name,

third_party/WebKit/Source/platform/loader/fetch/RawResource.cpp

@@ -340,7 +340,8 @@ static bool ShouldIgnoreHeaderForCacheReuse(AtomicString header_name) {
 static bool IsCacheableHTTPMethod(const AtomicString& method) {
   // Per http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.10,
   // these methods always invalidate the cache entry.
-  return method != "POST" && method != "PUT" && method != "DELETE";
+  return method != HTTPNames::POST && method != HTTPNames::PUT &&
+         method != "DELETE";
 }
 
 bool RawResource::CanReuse(const FetchParameters& new_fetch_parameters) const {

third_party/WebKit/Source/platform/network/http_names.json5

@@ -9,6 +9,7 @@
     "HEAD",
     "POST",
     "OPTIONS",
+    "PUT",
     "Accept",
     "Accept-CH",
     "Accept-CH-Lifetime",