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..f1774edc8b06a89962d957d1e4de622d3203d89a 100644
--- a/google_apis/google_api_keys.h
+++ b/google_apis/google_api_keys.h
@@ -73,6 +73,9 @@ std::string GetNonStableAPIKey();
 
 std::string GetRemotingAPIKey();
 
+// Sets the API key.
+void SetAPIKey(std::string api_key);

[Hiroshi Ichikawa, 2017/04/13 06:42:55]

Can you document that this must be called only before running any code using the
API key? I believe sdefresne@ or someone said that many code assumes the API key
is immutable. Same for below.

[Hiroshi Ichikawa, 2017/04/13 06:42:55]

const std::string& would be better. Same for below.

[jzw1, 2017/04/14 02:10:32]

Done.

[jzw1, 2017/04/14 02:10:32]

Done.

+
 // Represents the different sets of client IDs and secrets in use.
 enum OAuth2Client {
   CLIENT_MAIN,         // Several different features use this.
@@ -97,6 +100,12 @@ std::string GetOAuth2ClientID(OAuth2Client client);
 // in, e.g. URL-escaped if you use it in a URL.
 std::string GetOAuth2ClientSecret(OAuth2Client client);
 
+// Sets the client id for the specified client.
+void SetClientID(std::string client_id, OAuth2Client client);

[Hiroshi Ichikawa, 2017/04/13 06:42:55]

SetOAuth2ClientID would be better to be consistent with other function names
around. Same for below.

[jzw1, 2017/04/14 02:10:32]

Done.

+
+// Sets the client secret for the specified client.
+void SetClientSecret(std::string client_secret, OAuth2Client client);

[Roger Tawa OOO till Jul 10th, 2017/04/13 17:42:43]

As discussed over email, let's put all these SetXXX methods inside #ifdef for
iOS only.

Nit: could we reverse the order of the two args, since it is a mapping from
client --> client_id/client_secret?

Let's also rename the setters to be consistent with the getters.  So:

void SetOAuth2ClientID(...)
void SetOAuth2ClientSecret(...)

[jzw1, 2017/04/14 02:10:32]

Done.

+
 // Returns the auth token for the data reduction proxy.
 std::string GetSpdyProxyAuthValue();