Merge 32166 - A quick fix for Issue 3798....

Merge 32166 - A quick fix for Issue 3798.
Some Chinese IMEs insert whitespace characters (U+3000) instead of input characters while they are composing text. So, trimming these whitespace characters (at the beginning of an omnibox) prevents from inputting text on these IMEs. As a quick fix, this change prevent our AutocompleteEditViewWin::OnImeComposition() from starting autocomplete when an omnibox starts with whitespace characters.

BUG=3798
TEST=Type "google.com" on Omnibox, type "Tab" to start tabtosearch, type 'nihao' on Microsoft New Phonetic IME, and see we can see Chinese characters in the omnibox. 
Review URL: http://codereview.chromium.org/391070

TBR=hbono@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=32268