singing shira before a miracle occurs

What if a person is 100% sure that Hashem will do a miracle and save him from danger -- can/he say thanks to Hashem even before the miracle has occurred?  

The Emek Bracha quotes from R' Chaim that the answer is found directly in the pesukim, "V'ani b'chasdicha batachti yageil libi b'yeshuasecha," I have complete faith that Hashem will bring me salvation, "Ashira la'Hashem ki gamal alay," and I will sing praise to Hashem when he rescues me.  Even though I have complete faith that the miracle will occur, it is only after the fact, "ki gamal alay," that I sing shira, not beforehand.

The Mechilta on our parsha reads the pasuk, "Hashem yilachem lachem v'atem tacharishun?" as a question, not a statement.  You expect Hashem to do a miracle for you while you sit on the sidelines and do nothing?  Bnei Yisrael asked Moshe what they should do, and he answered that they should sing praises to Hashem.  

I can't find a Mechilta online, but here it is in Yalkut Shimoni:

 רַבִּי אוֹמֵר, ה׳ יִלָּחֵם לָכֶם הַמָּקוֹם יַעֲשֶׂה לָכֶם נִסִּים וּגְבוּרוֹת וְאַתֶּם תִּהְיוּ עוֹמְדִין וְשׁוֹתְקִין. אָמְרוּ יִשְׂרָאֵל לְמֹשֶׁה, מֹשֶׁה רַבֵּנוּ, מָה עָלֵינוּ לַעֲשׂוֹת. אָמַר לָהֶם, אַתֶּם תִּהְיוּ מְפָאֲרִין מְרוֹמְמִין וּמְשַׁבְּחִין וְכוּ׳. בְּאוֹתָהּ שָׁעָה פָּתְחוּ יִשְׂרָאֵל פִּיהֶם וְאָמְרוּ שִׁירָה, (להלן ט״ו:א׳) ״אָשִׁירָה לַה׳ כִּי גָאֹה גָּאָה״.

The Mechilta's reading that shira occurred before the miracle runs counter to simple pshat in the pesukim, but putting that aside, the Mechilta seems to undermine R' Chaim's argument.  According to the Mechilta, Klal Yisrael sang shira an anticipation of the splitting of Yam Suf; they didn't wait until after the fact, until the "ki gamal alay."

The Brisker Rav tries to defend R' Chaim by distinguishing between having emunah that a miracle will occur and being told by a navi like Moshe Rabeinu that a miracle will occur.  I think you need to explain why that distinction makes a difference, and secondly, where does it say that Moshe told Klal Yisrael that there would be a miracle like the splitting of the sea?