Expose way to set google api key through CWVWebView class method.

google_apis/google_api_keys.h

Index: google_apis/google_api_keys.h
diff --git a/google_apis/google_api_keys.h b/google_apis/google_api_keys.h
index e10078c330a142b8a3a01a9fba125d4dca75bb89..17973f0b073f20721c3d0d0437d46b6fea7f8f23 100644
--- a/google_apis/google_api_keys.h
+++ b/google_apis/google_api_keys.h
@@ -73,6 +73,12 @@ std::string GetNonStableAPIKey();
 
 std::string GetRemotingAPIKey();
 
+#if defined(OS_IOS)
+// Sets the API key. This should be called as early as possible before this
+// API key is even accessed. Currently only allowed on iOS.
+void SetAPIKey(const std::string& api_key);
+#endif
+
 // Represents the different sets of client IDs and secrets in use.
 enum OAuth2Client {
   CLIENT_MAIN,         // Several different features use this.
@@ -97,6 +103,16 @@ std::string GetOAuth2ClientID(OAuth2Client client);
 // in, e.g. URL-escaped if you use it in a URL.
 std::string GetOAuth2ClientSecret(OAuth2Client client);
 
+#if defined(OS_IOS)
+// Sets the client id for the specified client.

[Hiroshi Ichikawa, 2017/04/14 02:19:44]

Add "This should be called as early as possible..." comment here too.

[jzw1, 2017/04/14 02:28:52]

Done.

+void SetOAuth2ClientID(OAuth2Client client, const std::string& client_id);
+#endif
+
+#if defined(OS_IOS)
+// Sets the client secret for the specified client.

[Hiroshi Ichikawa, 2017/04/14 02:19:44]

Add "This should be called as early as possible..." comment here too.

[jzw1, 2017/04/14 02:28:52]

Done.

+void SetOAuth2ClientSecret(OAuth2Client client,
+                           const std::string& client_secret);
+#endif
 // Returns the auth token for the data reduction proxy.
 std::string GetSpdyProxyAuthValue();