Reland "Add remoting FTL API key"

This is a reland of c0cf050d

Original change's description:
> Add remoting FTL API key
>
> Add API key for remoting to use during the signaling process. Note that
> this key is only used by Chrome Remote Desktop and will not be used in
> the Chrome browser.
>
> Internal CL: https://chrome-internal-review.googlesource.com/c/chrome/google_apis/internal/+/831973
>
> Bug: 927962
> Change-Id: Iecfa48aebe1078a4a0c747f42711000d9155fc3f
> Reviewed-on: https://chromium-review.googlesource.com/c/1450409
> Reviewed-by: Joe Downing <joedow@chromium.org>
> Reviewed-by: Roger Tawa <rogerta@chromium.org>
> Auto-Submit: Yuwei Huang <yuweih@chromium.org>
> Commit-Queue: Roger Tawa <rogerta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#630352}

TBR=rogerta@chromium.org

Bug: 927962
Change-Id: I63c2e7e16621a01827609fab0c8969fd85b2399c
Reviewed-on: https://chromium-review.googlesource.com/c/1461306
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Auto-Submit: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630504}

google_apis/google_api_keys.cc

@@ -73,6 +73,10 @@
 #define GOOGLE_API_KEY_PHYSICAL_WEB_TEST DUMMY_API_TOKEN
 #endif
 
+#if !defined(GOOGLE_API_KEY_REMOTING_FTL)
+#define GOOGLE_API_KEY_REMOTING_FTL DUMMY_API_TOKEN
+#endif
+
 // These are used as shortcuts for developers and users providing
 // OAuth credentials via preprocessor defines or environment
 // variables.  If set, they will be used to replace any of the client
@@ -111,6 +115,11 @@ class APIKeyCache {
     api_key_non_stable_ = api_key_;
 #endif
 
+    api_key_remoting_ftl_ =
+        CalculateKeyValue(GOOGLE_API_KEY_REMOTING_FTL,
+                          STRINGIZE_NO_EXPANSION(GOOGLE_API_KEY_REMOTING_FTL),
+                          NULL, std::string(), environment.get(), command_line);
+
     std::string default_client_id =
         CalculateKeyValue(GOOGLE_DEFAULT_CLIENT_ID,
                           STRINGIZE_NO_EXPANSION(GOOGLE_DEFAULT_CLIENT_ID),
@@ -198,6 +207,7 @@ class APIKeyCache {
   void set_api_key(const std::string& api_key) { api_key_ = api_key; }
 #endif
   std::string api_key_non_stable() const { return api_key_non_stable_; }
+  std::string api_key_remoting_ftl() const { return api_key_remoting_ftl_; }
 
   std::string GetClientID(OAuth2Client client) const {
     DCHECK_LT(client, CLIENT_NUM_ITEMS);
@@ -293,6 +303,7 @@ class APIKeyCache {
 
   std::string api_key_;
   std::string api_key_non_stable_;
+  std::string api_key_remoting_ftl_;
   std::string client_ids_[CLIENT_NUM_ITEMS];
   std::string client_secrets_[CLIENT_NUM_ITEMS];
 };
@@ -312,6 +323,10 @@ std::string GetNonStableAPIKey() {
   return g_api_key_cache.Get().api_key_non_stable();
 }
 
+std::string GetFtlAPIKey() {
+  return g_api_key_cache.Get().api_key_remoting_ftl();
+}
+
 #if defined(OS_IOS)
 void SetAPIKey(const std::string& api_key) {
   g_api_key_cache.Get().set_api_key(api_key);

google_apis/google_api_keys.h

@@ -73,6 +73,10 @@ std::string GetAPIKey();
 // Non-stable channels may have a different Google API key.
 std::string GetNonStableAPIKey();
 
+// Retrieves the Chrome Remote Desktop FTL API key to be used during the
+// signaling process.
+std::string GetRemotingFtlAPIKey();
+
 #if defined(OS_IOS)
 // Sets the API key. This should be called as early as possible before this
 // API key is even accessed.